Highly Heat-Resistant Resin Composite Including Chemically Modified, Fine Cellulose Fibers

ABSTRACT

Provided is a resin composite having high mechanical properties which make the resin composite moldable into and usable as members for use in applications such as vehicle-mounted members and electrical materials. The resin composite comprises 0.5-40 mass % chemically modified, fine cellulose fibers and a resin, wherein the chemically modified, fine cellulose fibers have a pyrolysis initiation temperature (TD) of 270° C. or higher, a number-average fiber diameter of 10 nm or larger but less than 1 μm, and a degree of crystallinity of 60% or higher. In a preferred embodiment, the chemically modified, fine cellulose fibers have a coefficient of variation (CV) in DS unevenness ratio, DSs/DSt, of 50% or less, the DS unevenness ratio being the ratio of the modification degree (DSs) of the surface layers of the fibers to the modification degree (DSt) of the whole of the fibers.

FIELD

The present invention relates to a resin composite containing chemicallymodified fine cellulose fibers and having a high thermal decompositioninitiation temperature.

BACKGROUND

Resins are light and have excellent processing characteristics, and aretherefore widely used for a variety of purposes including automobilemembers, electrical and electronic parts, business machine housings,precision parts and the like. With resins alone, however, the mechanicalproperties and dimensional stability are often inadequate, and thereforeit is common to use composites of resins with different types ofinorganic materials.

Resin compositions comprising resins reinforced with reinforcingmaterials consisting of inorganic fillers such as glass fibers, carbonfibers, talc or clay have high specific gravity, and the obtained moldedresins thus have higher weight.

In recent years, cellulose nanofibers (CNF) have come into use as newreinforcing materials for resins.

In terms of simple properties, fine cellulose fibers are known to have ahigh elastic modulus similar to aramid fibers, and a lower linearexpansion coefficient than glass fibers. In addition, they exhibit a lowtrue density of 1.56 g/cm³, which is overwhelmingly lighter than glass(density: 2.4 to 2.6 g/cm³) or talc (density: 2.7 g/cm³) which are usedas common reinforcing materials for thermoplastic resins.

Fine cellulose fibers are obtained from a variety of sources, includingthose obtained from trees as starting materials, as well as from hemp,cotton, kenaf and cassava starting materials. Bacterial celluloses arealso known, typical of which is nata de coco. These natural resourcesthat can serve as starting materials are abundant throughout the Earth,and a great deal of effort has been focused on techniques for takingadvantage of fine cellulose fibers as fillers in resins, to allow themto be effectively utilized.

PTL 1 describes a technique of impacting wood pulp or the like in ahigh-pressure stream jet to obtain fine cellulose fibers, and thenderivatizing the fine cellulose fibers to improve the compatibilitybetween hydrophobic resins and the fine cellulose fibers.

In PTLs 2 to 4 there are described techniques of using an ionic liquidfor chemical modification (derivatization) of fine cellulose fibersobtained from defibrating treatment of a fiber starting material, tochemically modify the hydroxyl groups of the fine cellulose fibers andincrease the heat resistance.

PTL 5 describes a technique for chemically modifying fine cellulosefibers containing lignin to increase the heat resistance, whileincreasing the compatibility between the fine cellulose fibers andresins due to the lignin.

In PTLs 6 and 7 there are described techniques of adding cellulose pulpto a liquid mixture containing an aprotic solvent, a fine cellulosefiber chemical modifier and a catalyst component that promotes chemicalmodification, and carrying out continued stirring to prepare chemicallymodified fine cellulose fibers.

CITATION LIST Patent Literature

[PTL 1] International Patent Publication No. WO2016/010016

[PTL 2] Japanese Unexamined Patent Publication No. 2013-44076

[PTL 3] Japanese Unexamined Patent Publication No. 2013-43984

[PTL 4] Japanese Unexamined Patent Publication No. 2010-104768

[PTL 5] International Patent Publication No. WO2016/148233

[PTL 6] International Patent Publication No. WO2017/073700

[PTL 7] International Patent Publication No. WO2017/159823

SUMMARY Technical Problem

Using these prior art techniques can be expected to provide some degreeof effect by imparting certain physical properties to the resins, butfrom the viewpoint of obtaining heat resistance that can withstand usefor on-vehicle purposes, there is still a need to provide resincomposites with even higher heat resistance.

The problem to be solved by one aspect of the present invention is toprovide a resin composite that has high mechanical properties, and thatis able to withstand casting and use for members to be used foron-vehicle purposes.

Solution to Problem

Specifically, the present invention encompasses the following aspects.

[1] A resin composite containing 0.5 to 40 mass % of chemically modifiedfine cellulose fibers, and a resin, wherein the chemically modified finecellulose fibers have:

a thermal decomposition initiation temperature (T_(D)) of 270° C. orhigher,

a number-average fiber diameter of 10 nm or greater and less than 1 μm,and

a degree of crystallinity of 60% or higher.

[2] The resin composite according to aspect 1, wherein the chemicallymodified fine cellulose fibers are dispersed in a resin composite in theform of a dispersion comprising a dispersion stabilizer and thechemically modified fine cellulose fibers dispersed in the dispersionstabilizer, and the content of the chemically modified fine cellulosefibers in the dispersion is 10 to 99 mass %.

[3] The resin composite according to aspect 1 or 2, wherein thedispersion stabilizer is at least one selected from the group consistingof surfactants and organic compounds with a boiling point of 160° C. orhigher.

[4] The resin composite according to any one of aspects 1 to 3, whereinthe resin is at least one type selected from the group consisting ofthermoplastic resins, thermosetting resins and photocuring resins.

[5] The resin composite according to aspect 4, wherein the resin is athermoplastic resin.

[6] The resin composite according to any one of aspects 1 to 5, whereinthe resin is at least one selected from the group consisting ofpolyolefin-based resins, polyacetate-based resins, polycarbonate-basedresins, polyamide-based resins, polyester-based resins, polyphenyleneether-based resins and acrylic-based resins.

[7] A resin composite according to any one of aspects 1 to 6, whereinthe melting point of the resin is 220° C. or higher.

[8] The resin composite according to any one of aspects 1 to 7, whereinthe linear coefficient of thermal expansion (CTE) of the resin compositeis 80 ppm/k or smaller.

[9] The resin composite according to any one of aspects 1 to 8, whereinthe weight-average molecular weight (Mw) of the chemically modified finecellulose fibers is 100,000 or greater, and the ratio (Mw/Mn) of theweight-average molecular weight (Mw) and number-average molecular weight(Mn) is 6 or lower.

[10] The resin composite according to any one of aspects 1 to 9, whereinthe average degree of substitution of hydroxyl groups of the chemicallymodified fine cellulose fibers is 0.5 or greater.

[11] The resin composite according to any one of aspects 1 to 10,wherein the chemically modified fine cellulose fibers are esterifiedfine cellulose fibers.

[12] The resin composite according to any one of aspects 1 to 11,wherein the degree of modification, as defined by the ratio of the peakintensity of the absorption band of the acyl group C═O with respect tothe peak intensity of the absorption band of C—H on the cellulosebackbone chain, in total reflection-infrared absorption spectrometry ofthe chemically modified fine cellulose fibers (the IR index 1370), is0.8 or greater.

[13] The resin composite according to any one of aspects 1 to 12,wherein the degree of modification, as defined by the ratio of the peakintensity of the absorption band of the acyl group C═O with respect tothe peak intensity of the absorption band of C—O on the cellulosebackbone chain, in total reflection-infrared absorption spectrometry ofthe chemically modified fine cellulose fibers (the IR index 1030), is0.13 or greater.

[14] The resin composite according to any one of aspects 1 to 13,wherein the coefficient of variation (CV) of the DS non-uniformity ratio(DSs/DSt), as the ratio of the degree of modification (DSs) of the fibersurface with respect to the degree of modification (DSt) of the entirechemically modified fine cellulose fibers, is 50% or lower.

[15] The resin composite according to any one of aspects 1 to 14,wherein the number-average fiber diameter of the chemically modifiedfine cellulose fibers is 50 nm to 300 nm.

[16] The resin composite according to any one of aspects 1 to 15,wherein the content of the alkali-soluble portion of the chemicallymodified fine cellulose fibers is 12 mass % or lower.

[17] The resin composite according to any one of aspects 1 to 16,wherein the average content of the acid-insoluble component per unitspecific surface area of the chemically modified fine cellulose fibersis 1.0 mass %·g/m² or lower.

[18] Chemically modified fine cellulose fibers wherein theweight-average molecular weight (Mw) is 100,000 or higher, the ratio(Mw/Mn) of the weight-average molecular weight (Mw) and number-averagemolecular weight (Mn) is 6 or lower, the alkali-soluble portion contentis 12 mass % or lower and the degree of crystallinity is 60% or higher.

[19] The chemically modified fine cellulose fibers according to aspect18, wherein the thermal decomposition initiation temperature (T_(D)) is270° C. or higher and the number-average fiber diameter is 10 nm orgreater and less than 1 μm.

[20] The chemically modified fine cellulose fibers according to aspect18 or 19, which are esterified fine cellulose fibers.

[21] The chemically modified fine cellulose fibers according to any oneof aspects 18 to 20, wherein the average degree of substitution ofhydroxyl groups is 0.5 or greater.

[22] The chemically modified fine cellulose fibers according to any oneof aspects 18 to 21, wherein the coefficient of variation (CV) of the DSnon-uniformity ratio (DSs/DSt), as the ratio of the degree ofmodification (DSs) of the fiber surface with respect to the degree ofmodification (DSt) of the entire chemically modified fine cellulosefibers, is 50% or lower.

[23] The chemically modified fine cellulose fibers according to any oneof aspects 18 to 22, wherein the average content of the acid-insolublecomponent per unit specific surface area of the chemically modified finecellulose fibers is 1.0 mass %·g/m² or lower.

[24] A method for producing chemically modified fine cellulose fibers,which includes: defibrating a cellulose starting material having aweight-average molecular weight (Mw) of 100,000 or greater, a ratio(Mw/Mn) of weight-average molecular weight (Mw) and number-averagemolecular weight (Mn) of 6 or lower and an alkali-soluble content of 12mass % or lower, in a dispersion that includes an aprotic solvent, toobtain fine cellulose fibers, and adding a modifying agent-containingsolution to the dispersion to modify the fine cellulose fibers, therebyobtaining chemically modified fine cellulose fibers having aweight-average molecular weight (Mw) of 100,000 or greater, a ratio(Mw/Mn) of weight-average molecular weight (Mw) and number-averagemolecular weight (Mn) of 6 or lower, an alkali-soluble content of 12mass % or lower and a degree of crystallinity of 60% or higher.

[25] The method according to aspect 24, wherein the thermaldecomposition initiation temperature (T_(D)) of the chemically modifiedfine cellulose fibers is 270° C. or higher and the number-average fiberdiameter is 10 nm or greater and less than 1 μm.

[26] The method according to aspect 24 or 25, wherein the aproticsolvent is dimethyl sulfoxide, and the modifying agent is vinyl acetateor acetic anhydride.

[27] A resin composite containing 0.5 to 40 mass % of chemicallymodified fine cellulose fibers according to any one of aspects 18 to 23,and a resin.

[28] A resin composite containing 0.5 to 40 mass % of chemicallymodified fine cellulose fibers and a resin, wherein the DSnon-uniformity ratio (DSs/DSt), as the ratio of the degree ofmodification (DSs) of the fiber surfaces with respect to the degree ofmodification (DSt) of the entire chemically modified fine cellulosefibers, is 1.1 or greater, and the coefficient of variation (CV) of theDS non-uniformity ratio (DSs/DSt) is 50% or lower.

[29] A method for producing a resin composite containing 0.5 to 40 mass% of chemically modified fine cellulose fibers, and a resin, wherein themethod includes:

a defibrating step in which a cellulose starting material is defibratedin a dispersion that includes the cellulose starting material and anaprotic solvent but essentially does not include an ionic liquid orsulfuric acid, to obtain fine cellulose fibers,

a modifying step in which a solution that includes a modifying agent isadded to the dispersion for chemical modification of the fine cellulosefibers, to obtain chemically modified fine cellulose fibers, and

a kneading step in which the chemically modified fine cellulose fibersand the resin are kneaded,

the DS non-uniformity ratio (DSs/DSt), as the ratio of the degree ofmodification (DSs) of the fiber surfaces with respect to the degree ofmodification (DSt) of the entire chemically modified fine cellulosefibers, is 1.1 or greater, and the coefficient of variation (CV) of theDS non-uniformity ratio (DSs/DSt) is 50% or lower.

[30] A method for producing a resin composite according to any one ofaspects 1 to 17, 27 and 28, wherein the method includes:

a step of defibrating cellulose in a dispersion containing a cellulosestarting material with a cellulose purity of 85 mass % or greater, andan aprotic solvent, to obtain fine cellulose fibers,

a step of adding a solution containing a modifying agent to thedispersion to modify the fine cellulose fibers, thereby obtainingchemically modified fine cellulose fibers having a thermal decompositioninitiation temperature (T_(D)) of 270° C. or higher, a number-averagefiber diameter of 10 nm or greater and less than 1 μm, and a degree ofcrystallinity of 60% or higher, and

a step of mixing the chemically modified fine cellulose fibers with aresin.

[31] The method according to aspect 29 or 30, wherein the aproticsolvent is dimethyl sulfoxide, and the modifying agent is vinyl acetateor acetic anhydride.

[32] A member for an automobile, comprising a resin composite accordingto any one of aspects 1 to 17, 27 and 28.

[33] A member for an electronic product, comprising a resin compositeaccording to any one of aspects 1 to 17, 27 and 28.

Advantageous Effects of Invention

The resin composite according to one aspect of the invention can havehigh mechanical properties, and can withstand casting and use formembers to be used for on-vehicle purposes.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an illustration of methods for measuring thermal decompositioninitiation temperature (T_(D)) and 1% weight reduction temperature(T_(1%)).

FIG. 2 is an illustration of a method for calculating the IR index 1370and IR index 1030.

FIG. 3 is a SEM image of the chemically modified fine fibers 1-1obtained in Production Example 1-1 of Example I.

FIG. 4 is a SEM image of the chemically modified fine fibers 2-1obtained in Example 2-1 of Example II.

DESCRIPTION OF EMBODIMENTS

Embodiments for carrying out the invention (hereunder referred to as“the embodiments”) will now be explained in detail. The presentinvention is not limited to the embodiments described below, however,and various modifications may be implemented within the scope of thegist thereof.

First Embodiment

The first embodiment, as one aspect of the invention, provides a resincomposite having a thermal decomposition initiation temperature (T_(D))of 270° C. or higher, a number-average fiber diameter of 10 nm orgreater and less than 1 μm, and comprising chemically modified finecellulose fibers. According to one aspect, the resin composite comprisesthe chemically modified fine cellulose fibers at 0.5 to 40 mass %. Alsoaccording to one aspect, the chemically modified fine cellulose fibershave a degree of crystallinity of 60% or higher.

The term “chemically modified fine cellulose fibers” (also referred tothroughout the present disclosure as “chemically modified fine fibers”)means fine cellulose fibers of which at least some of the hydroxylgroups in the cellulose backbone have been modified. According to atypical aspect, the cellulose as a whole is not chemically modified, andthe chemically modified fine fibers retain the crystal structure of thefine cellulose fibers before chemical modification. The crystallinestructure of either or both type I cellulose and type II cellulose canbe confirmed by analysis of the chemically modified fine fibers by XRD,for example.

The resin composite comprises chemically modified fine fibers and aresin. The resin composite may also include other components (forexample, an inorganic filler). The content of the chemically modifiedfine fibers in the resin composite of this embodiment is 0.5 to 40 mass%, preferably 2 to 30 mass % and more preferably 3 to 20 mass %,according to one aspect, from the viewpoint of obtaining a resincomposite with excellent heat resistance.

The method of removing the chemically modified fine fibers from theresin composite may be a method of using a resin solubilizer to extractthe resin component, and then carrying out purification and cleaning toextract the chemically modified fine fibers in dry form or as an aqueousdispersion, without loss of their properties. Examples of resinsolubilizers include 1,2,4-trichlorobenzene for polyolefins orhexafluoro-2-isopropanol for 1,2-dichlorobenzene and polyamides,although the resin solubilizer is not limited to these.

From the viewpoint of heat resistance of the resin composite, thenumber-average fiber diameter of the chemically modified fine fibers inthe resin composite according to one aspect is 10 nm or greater and lessthan 1 μm, preferably 10 nm to 800 nm, more preferably 10 nm to 500 nm,even more preferably 20 nm to 300 nm and most preferably 50 nm to 300nm. The length/diameter ratio (L/D ratio) of the chemically modifiedfine fibers, according to one aspect, is 30 or greater, preferably 100or greater, more preferably 200 or greater, even more preferably 300 orgreater and most preferably 500 or greater.

The weight-average molecular weight (Mw) of the chemically modified finefibers of this embodiment, and the chemically modified fine fibers inthe resin composite, is preferably 100,000 or greater and morepreferably 200,000 or greater. The ratio (Mw/Mn) of the weight-averagemolecular weight and number-average molecular weight (Mn) of thechemically modified fine fibers of this embodiment, and the chemicallymodified fine fibers in the resin composite, is preferably 6 or lowerand more preferably 5.4 or lower. A higher weight-average molecularweight means a lower number of terminal groups of the cellulosemolecules. Since the ratio (Mw/Mn) of the weight-average molecularweight and number-average molecular weight represents the width of themolecular weight distribution, a smaller Mw/Mn means a lower number ofends of cellulose molecules. Since the ends of the cellulose moleculesare origins for thermal decomposition, a high weight-average molecularweight is also a more narrow width of molecular weight distribution, andthus high heat resistance for the fine cellulose fibers and for theresin composite of the fine cellulose fibers and resin. Theweight-average molecular weight (Mw) of the chemically modified finefibers may be 600,000 or lower, or 500,000 or lower, for example, fromthe viewpoint of greater availability of the cellulose startingmaterial. The ratio (Mw/Mn) of the weight-average molecular weight andnumber-average molecular weight (Mn) may be 1.5 or greater or 2 orgreater, from the viewpoint of easier production of the chemicallymodified fine fibers. The Mw can be controlled to within this range byselecting a cellulose starting material having the corresponding Mw, orby carrying out appropriate physical treatment and/or chemical treatmentof the cellulose starting material. The Mw/Mn ratio can also becontrolled to within this range by selecting a cellulose startingmaterial having the corresponding Mw/Mn ratio, or by carrying outappropriate physical treatment and/or chemical treatment of thecellulose starting material. Examples of physical treatment for controlof both the Mw and Mw/Mn include physical treatment by application ofmechanical force, such as dry grinding or wet grinding with amicrofluidizer, ball mill or disk mill, for example, or impacting,shearing, sliding or abrasion with a crusher, homomixer, high-pressurehomogenizer or ultrasonic device, for example, while examples ofchemical treatment include digestion, bleaching, acid treatment andregenerated cellulose treatment.

The weight-average molecular weight and number-average molecular weightof the cellulose referred to here are the values determined afterdissolving the cellulose in lithium chloride-addedN,N-dimethylacetamide, and then performing gel permeation chromatographywith N,N-dimethylacetamide as the solvent.

The thermal decomposition initiation temperature (T_(D)) of thechemically modified fine fibers in the resin composite, according to oneaspect, is 270° C. or higher, preferably 275° C. or higher, morepreferably 280° C. or higher and even more preferably 285° C. or higher,from the viewpoint of allowing the desired heat resistance andmechanical strength to be exhibited for on-vehicle purposes. While ahigher thermal decomposition initiation temperature is preferred, it isalso no higher than 320° C. or no higher than 300° C. from the viewpointof easier production of the chemically modified fine fibers.

For the purpose of the present disclosure, the T_(D) value is the valuedetermined from a graph of thermogravimetry (TG) analysis where theabscissa is temperature and the ordinate is weight residual ratio %, asshown in the diagram of FIG. 1 (FIG. 1(B) shows a magnified view of FIG.1(A)). Starting from the weight of chemically modified fine fibers at150° C. (with essentially all of the moisture content removed) (0 wt %weight reduction) and increasing the temperature, a straight line isobtained running through the temperature at 1 wt % weight reduction(T_(1%)) and the temperature at 2 wt % weight reduction (T_(2%)). Thetemperature at the point of intersection between this straight line anda horizontal (baseline) running through the origin at weight reduction 0wt %, is defined as T_(D).

The 1% weight reduction temperature (T_(1%)) is the temperature at 1 wt% weight reduction with the 150° C. weight as the origin, aftercontinuous temperature increase by the method for T_(D) described above.

The 250° C. weight reduction of the chemically modified fine fibers inthe resin composite (T_(250° C.)) is the weight reduction after thechemically modified fine fibers have been kept for 2 hours at 250° C.under a nitrogen flow, in TG analysis.

According to one aspect, the chemically modified fine fibers of thisembodiment have a degree of crystallinity of 60% or higher. If thedegree of crystallinity is within this range, the mechanical propertiesof the chemically modified fine fibers themselves (especially thestrength and dimensional stability) will be high, tending to result inhigh strength and dimensional stability of the resin compositecomprising the chemically modified fine fibers dispersed in the resin. Ahigh degree of crystallinity means fewer amorphous sections, andtherefore a high degree of crystallinity is also preferred from theviewpoint of heat resistance, considering that amorphous sections canact as origins of deterioration.

The degree of crystallinity of the chemically modified fine fibers ispreferably 65% or higher, more preferably 70% or higher and mostpreferably 80% or higher. Since a higher degree of crystallinity for thechemically modified fine fibers tends to be preferable the upper limitis not particularly restricted, but from the viewpoint of productivityit is preferably an upper limit of 99%.

When the cellulose is type I cellulose crystals (derived from naturalcellulose), the degree of crystallinity referred to here is thatdetermined by the following formula, from the diffraction pattern(20/deg.=10 to 30) obtained by measurement of the sample by wide-angleX-ray diffraction, based on the Segal method.

Degree of crystallinity(%)=[I ₍₂₀₀₎ −I _((amorphous))]/I ₍₂₀₀₎×100

I₍₂₀₀₎: Diffraction peak intensity at 200 plane (2θ=22.5°) of type Icellulose crystal I_((amorphous)): Amorphous halo peak intensity fortype I cellulose crystal, peak intensity at angle of 4.5° lower thandiffraction angle at 200 plane (2θ=18.0°).

When the cellulose is type II cellulose crystals (derived fromregenerated cellulose), the degree of crystallinity is determined by thefollowing formula, from the absolute peak intensity h0 at 20=12.6°attributed to the (110) plane peak of the type II cellulose crystal, andthe peak intensity h1 from the baseline for the plane spacing, inwide-angle X-ray diffraction.

Degree of crystallinity(%)=h1/h0×100

The known crystalline forms of cellulose include type I, type II, typeIII and type IV, among which type I and type II are most commonly used,whereas type III and type IV are not commonly used on an industrialscale but have been obtained on a laboratory scale. The chemicallymodified fine fibers are preferably chemically modified fine fiberscontaining type I cellulose crystals or type II cellulose crystals, forrelatively high mobility in terms of structure and to obtain a resincomposite with a lower linear coefficient of thermal expansion and moreexcellent strength and elongation when subjected to stretching orbending deformation, by dispersion of the chemically modified finefibers in the resin, and more preferably the chemically modified finefibers contain type I cellulose crystals and have a degree ofcrystallinity of 60% or higher.

The chemically modified fine fibers of this embodiment have the hydroxylgroups of the cellulose molecules on the surface of the fine cellulosefibers chemically modified by a cellulose modifying agent. The chemicalmodification is preferably esterification and more preferablyacetylation.

In the chemically modified fine fibers of this embodiment, a largeamount of acid-insoluble component including lignin may lead todiscoloration by the heat of processing, and therefore the mean contentof the acid-insoluble component in the chemically modified fine fibersis preferably as low as possible. Specifically, it is preferably lessthan 10 mass %, more preferably 8 mass % or lower, even more preferably7 mass % or lower, yet more preferably 6 mass % or lower and mostpreferably 5 mass % or lower.

The mean content of the acid-insoluble component is measured using theKlason method, described in non-patent literature (Mokushitsu KagakuJikken Manual, ed. The Japan Wood Research Society, pp. 92-97, 2000).The sample is stirred in the sulfuric acid solution to dissolve thecellulose and alkali-soluble component, and then filtered with glassfiber filter paper, and the obtained residue is used as theacid-insoluble component. The acid-insoluble component content iscalculated from the weight of the acid-insoluble component, and theaverage of the acid-insoluble component content calculated for threesamples is recorded as the mean content of the acid-insoluble component.

The mean content for the acid-insoluble component in the chemicallymodified fine fibers of this embodiment can be calculated from the meancontent for the acid-insoluble component in the cellulose startingmaterial used for production of the chemically modified fine fibers.

The mean content for the acid-insoluble component with respect to thespecific surface area of the chemically modified fine fibers isespecially important in terms of the relationship between theacid-insoluble component and the dynamic properties of the resincomposite. Specifically, a low abundance of acid-insoluble component atthe interface between the cellulose fiber surfaces and the resin helpsto avoid loss of the dynamic properties of the resin composite that isreinforced by the chemically modified fine fibers.

The mean content for the acid-insoluble component per unit specificsurface area of the chemically modified fine fibers is preferably 1.0mass %·g/m² or lower, more preferably 0.6 mass %·g/m² or lower, evenmore preferably 0.5 mass %·g/m² or lower, even more preferably 0.4 mass%·g/m² or lower and most preferably 0.2 mass %·g/m² or lower. It ispreferred to have a lower mean content for the acid-insoluble component,and more preferably it is 0 mass %·g/m². The specific surface area ofthe chemically modified fine fibers can be calculated as the BETspecific surface area obtained using a specific surface area/poredistribution measuring apparatus (by Quantachrome Instruments) with theprogram of the apparatus, after measuring the nitrogen gas adsorption atthe boiling point of liquid nitrogen at five points (multipoint method)in a relative vapor pressure (P/P₀) range of 0.05 to 0.2, for a poroussheet sample of the chemically modified fine fibers.

According to one aspect, the alkali-soluble portion content of thechemically modified fine fibers is 12 mass % or lower, preferably 11mass % or lower and even more preferably 8 mass % or lower. Thealkali-soluble portion for the present disclosure also encompassesn-cellulose and γ-cellulose, in addition to hemicellulose. Thealkali-soluble portion is understood by those skilled in the art toconsist of the components that are obtained as the alkali-solubleportion of holocellulose (that is, the components other than α-cellulosein the holocellulose), upon solvent extraction and chlorine treatment ofa plant (such as wood). Since the alkali-soluble portion consists ofhydroxyl group-containing polysaccharides with poor heat resistance,which can lead to inconveniences such as decomposition when subjected toheat, yellowing due to heat aging and reduced strength of the cellulosefibers, it is preferred to have a lower alkali-soluble portion contentin the chemically modified fine fibers. The alkali-soluble portioncontent in the chemically modified fine fibers is most preferably 0 mass%, but it may be 3 mass % or greater or 6 mass % or greater from theviewpoint of easier availability of the cellulose starting material.

The alkali-soluble portion content can be determined by a methoddescribed in non-patent literature (Mokushitsu Kagaku Jikken Manual, ed.The Japan Wood Research Society, pp. 92-97, 2000), subtracting theα-cellulose content from the holocellulose content (Wise method). Thealkali-soluble portion content in the chemically modified fine fiberswill usually be essentially the same as the alkali-soluble portioncontent in the cellulose starting material used for production of thechemically modified fine fibers (that is, it may be assumed that thereis essentially no selective removal of the alkali-soluble portion underordinary conditions for chemical modification (typically weakly acidicto neutral pH)). According to one aspect, the value of thealkali-soluble portion content of the cellulose starting material may beconsidered to be the alkali-soluble portion content in the chemicallymodified fine fibers.

The chemically modified fine fibers of this embodiment, and theirproduction method, as well as the resin composite and its productionmethod, will now be described.

The cellulose fibers used as starting material for the chemicallymodified fine fibers (also referred to as “cellulose starting material)may be natural cellulose or regenerated cellulose. Natural celluloseincludes wood pulp obtained from wood sources (broadleaf trees orconifers), nonwood pulp obtained from non-wood sources (cotton, bamboo,hemp, bagasse, kenaf, cotton linter, sisal and straw), and cellulosefiber aggregates obtained from sources such as animals (such as seasquirts) and algae, microbes (such as acetic acid bacteria) andmicrobial products. Regenerated cellulose for use may be cut yarn ofregenerated cellulose fibers (such as viscose, cupra and Tencel), cutyarn of cellulose derivative fibers, and superfine yarn of regeneratedcellulose or cellulose derivatives, obtained by electrospinning methods.These starting materials may have their fiber diameters, fiber lengthsor fibrilization degrees adjusted by beating, fibrilization ormicronization with mechanical force using a grinder or refiner, or theymay be subjected to bleaching and purification with chemicals, or theirnon-cellulose contents such as lignin or hemicellulose may also beadjusted, as necessary.

The content of acid-insoluble components (especially lignin) in thecellulose starting material is preferably as low as possible. Themodifying agent used for chemical modification of the fine cellulosefibers is consumed by secondary reaction with the acid-insolublecomponent, often resulting in residue of the secondary reaction productsin the fine cellulose fibers after chemical modification. This lowersproduction process yield and hampers quality control, and also causesyellowing by heat during production of the resin composite. From thisviewpoint, the content of the acid-insoluble component in the cellulosestarting material is preferably less than 10 mass %, more preferably 8mass % or lower, even more preferably 7 mass % or lower, yet morepreferably 6 mass % or lower and most preferably 5 mass % or lower. Thecontent of the acid-insoluble component in the cellulose startingmaterial is most preferably 0 mass %, but it may be 1 mass % or greater,greater or 2 mass % or greater, 3 mass % or greater or 4 mass % orgreater, from the viewpoint of easier availability of the cellulosestarting material.

The content of the alkali-soluble portion (especially hemicellulose) inthe cellulose starting material is preferably as low as possible. Themodifying agent used for chemical modification of the fine cellulosefibers is consumed by secondary reaction with the alkali-solubleportion, often resulting in residue of the secondary reaction productsin the fine cellulose fibers after chemical modification. This lowersproduction process yield and hampers quality control, and also causesyellowing by heat during production of the resin composite. From thisviewpoint, the content of the alkali-soluble portion (especiallyhemicellulose) in the cellulose starting material is preferably 13 mass% or lower, more preferably 12 mass % or lower, even more preferably 11mass % or lower, yet more preferably 8 mass % or lower and mostpreferably 5 mass % or lower. The content of the alkali-soluble portion(especially hemicellulose) in the cellulose starting material is mostpreferably 0 mass %, but it may be 3 mass % or greater or 6 mass % orgreater from the viewpoint of easier availability of the cellulosestarting material.

The modifying agent used may be a compound that reacts with the hydroxylgroups of cellulose, and esterifying agents, etherifying agents andsilylating agents may be mentioned. Esterifying agents are particularlypreferred. Preferred esterifying agents are acid halides, acidanhydrides and vinyl carboxylate esters.

An acid halide may be one or more selected from the group consisting ofcompounds represented by the following formula (1).

R1-C(═O)—X  (1)

(In the formula, R1 represents an alkyl group of 1 to 24 carbon atoms,an alkylene group of 1 to 24 carbon atoms, a cycloalkyl group of 3 to 24carbon atoms or an aryl group of 6 to 24 carbon atoms, and X is Cl, Bror I.) Specific examples of acid halides include acetyl chloride, acetylbromide, acetyl iodide, propionyl chloride, propionyl bromide, propionyliodide, butyryl chloride, butyryl bromide, butyryl iodide, benzoylchloride, benzoyl bromide and benzoyl iodide, with no limitation tothese. Acid chlorides are preferably used among these from the viewpointof reactivity and handleability. For reaction of an acid halide, one ormore alkaline compounds may also be added to neutralize the acidicby-products, while simultaneously acting as a catalyst. Specificexamples of alkaline compounds include: tertiary amine compounds such astriethylamine and trimethylamine; and nitrogen-containing aromaticcompounds such as pyridine and dimethylaminopyridine; with no limitationto these.

Any suitable acid anhydride may be used as an acid anhydride. Examplesinclude saturated aliphatic monocarboxylic anhydrides of acetic acid,propionic acid, (iso)butyric acid and valeric acid; unsaturatedaliphatic monocarboxylic anhydrides of (meth)acrylic acid and oleicacid; alicyclic monocarboxylic anhydrides of cyclohexanecarboxylic acidand tetrahydrobenzoic acid; aromatic monocarboxylic anhydrides ofbenzoic acid and 4-methylbenzoic acid; dibasic carboxylic anhydrides,for example: saturated aliphatic dicarboxylic acid anhydrides such assuccinic anhydride and adipic anhydride, unsaturated aliphaticdicarboxylic anhydrides such as maleic anhydride and itaconic anhydride,alicyclic dicarboxylic acid anhydrides such as1-cyclohexene-1,2-dicarboxylic anhydride, hexahydrophthalic anhydrideand methyltetrahydrophthalic anhydride, and aromatic dicarboxylicanhydrides such as phthalic anhydride and naphthalic anhydride; andtribasic or greater polybasic carboxylic anhydrides, for example:polycarboxylic acid (anhydrides) such as trimellitic anhydride andpyromellitic anhydride. The catalyst added for reaction of an acidanhydride may be one or more acidic compounds such as sulfuric acid,hydrochloric acid or phosphoric acid, or Lewis acids such as metalchlorides or metal triflates, or alkaline compounds such astriethylamine or pyridine.

Preferred vinyl carboxylate esters are vinyl carboxylate estersrepresented by the following formula (2):

R—COO—CH═CH₂:  formula (2)

{where R is an alkyl group of 1 to 24 carbon atoms, an alkylene group of1 to 24 carbon atoms, a cycloalkyl group of 3 to 24 carbon atoms or anaryl group of 6 to 24 carbon atoms}. Vinyl carboxylate esters are morepreferably one or more selected from the group consisting of vinylacetate, vinyl propionate, vinyl butyrate, vinyl caproate, vinylcyclohexanecarboxylate, vinyl caprylate, vinyl caprate, vinyl laurate,vinyl myristate, vinyl palmitate, vinyl stearate, vinyl pivalate, vinylocrylate, divinyl adipate, vinyl methacrylate, vinyl crotonate, vinylpivalate, vinyl ocrylate, vinyl benzoate and vinyl cinnamate. Duringesterification reaction with a vinyl carboxylate ester, one or morecatalysts may be added that are selected from the group consisting ofalkali metal hydroxides, alkaline earth metal hydroxides, primary totertiary amines, quaternary ammonium salts, imidazole and itsderivatives, pyridine and its derivatives, and alkoxides.

Alkali metal hydroxides and alkaline earth metal hydroxides includesodium hydroxide, potassium hydroxide, lithium hydroxide, calciumhydroxide and barium hydroxide.

Primary to tertiary amines are primary amines, secondary amines andtertiary amines, specific examples of which include ethylenediamine,diethylamine, proline, N,N,N′,N′-tetramethylethylenediamine,N,N,N′,N′-tetramethyl-1,3-propanediamine,N,N,N′,N′-tetramethyl-1,6-hexanediamine,tris(3-dimethylaminopropyl)amine, N,N-dimethylcyclohexylamine andtriethylamine.

Imidazole and its derivatives include 1-methylimidazole,3-aminopropylimidazole and carbonyldiimidazole.

Pyridine and its derivatives include N,N-dimethyl-4-aminopyridine andpicoline.

Alkoxides include sodium methoxide, sodium ethoxide andpotassium-t-butoxide.

Particularly preferred among these esterification reactants are one ormore selected from the group consisting of acetic anhydride, propionicanhydride, butyric anhydride, vinyl acetate, vinyl propionate and vinylbutyrate, among which acetic anhydride and vinyl acetate are especiallypreferred from the viewpoint of reaction efficiency.

According to one aspect, the chemically modified fine cellulose fiberscan be obtained by defibrating a cellulose starting material, having aweight-average molecular weight (Mw) of 100,000 or greater, a ratio(Mw/Mn) of weight-average molecular weight (Mw) and number-averagemolecular weight (Mn) of 6 or lower and an alkali-soluble portioncontent of 12 mass % or lower, in a dispersion containing an aproticsolvent, to obtain fine cellulose fibers, or adding a solutioncontaining a modifying agent to the dispersion to modify the finecellulose fibers, and the obtained chemically modified fine fibers mayhave a thermal decomposition initiation temperature (T_(D)) of 270° C.or higher, a number-average fiber diameter of 10 nm or greater and lessthan 1 μm and a degree of crystallinity of 60% or higher. Chemicalmodification after preparation of fine cellulose fibers by defibratingis advantageous from the viewpoint of lowering the coefficient ofvariation of the DS non-uniformity ratio (DSs/DSt).

The method for reducing the maximum fiber diameter in order to convertthe cellulose starting material to fine cellulose fibers is notparticularly restricted, but it is preferred for the defibratingtreatment conditions (creation of the shear field or the size of theshear field) to be as efficient as possible. In particular, adefibrating solution containing an aprotic solvent is impregnated with acellulose starting material with a cellulose purity of 85 mass % orgreater, and swelling of the cellulose is induced in a short period oftime, while merely applying the energy of a small degree of stirring andshear for micronization of the cellulose. Also, a cellulose modifyingagent may be added immediately after defibrating, to obtain chemicallymodified fine fibers. This method is preferred from the viewpoint ofproduction efficiency and refining efficiency (i.e. the high purity ofthe chemically modified fine fibers), as well as the physical propertiesof the resin composite.

The aprotic solvent may be an alkyl sulfoxide, an alkylamide orpyrrolidone, for example. Any of these solvents may be used alone or incombinations of two or more.

Examples of alkyl sulfoxides include di-C1-4 alkyl sulfoxides such asdimethyl sulfoxide (DMSO), methylethyl sulfoxide and diethyl sulfoxide.

Examples of alkylamides include N,N-di-C1-4 alkylformamides such asN,N-dimethylformamide (DMF) and N,N-diethylformamide; and N,N-di-C1-4alkylacetamides such as N,N-dimethylacetamide (DMAc) andN,N-diethylacetamide.

Examples of pyrrolidones include pyrrolidones such as 2-pyrrolidone and3-pyrrolidone; and N—C1-4 alkylpyrrolidones such asN-methyl-2-pyrrolidone (NMP).

Any of these aprotic solvents may be used alone or in combinations oftwo or more. Among these aprotic solvents using DMSO (29.8), DMF (26.6),DMAc (27.8) and NMP (27.3) (the numerals in parentheses indicating thedonor numbers), and especially DMSO, allows chemically modified finefibers with a high thermal decomposition initiation temperature to bemore efficiently produced. While the action mechanism for this is notcompletely understood, it is theorized to be due to homogeneousmicroswelling of the cellulose starting material in the aprotic solvent.

When the cellulose starting material for the fine cellulose fibersswells in the aprotic solvent, the aprotic solvent rapidly permeates thefibrils composing the starting material and swells them, such that themicrofibrils are converted to a fine defibrated state. After this statehas been created, chemical modification is carried out to promotechemical modification in a homogeneous manner throughout all of themicrofilaments, by which, presumably, high heat resistance is obtained.In addition, the microfibrillated chemically modified fine fibersmaintain a high degree of crystallinity, and allow high mechanicalproperties and excellent dimensional stability (especially a very lowlinear coefficient of thermal expansion) to be obtained when compositedwith resins.

On the other hand, when fine cellulose fibers produced by defibrating inwater or a protic solvent have been chemically modified by replacementwith an aprotic solvent, the improvement in heat resistance by thechemical modification is somewhat attenuated. While the action mechanismfor this is not completely understood, it is conjectured that the highliquid-absorbing property of cellulose hampers complete replacement tothe aprotic solvent, and therefore homogeneous chemical modificationdoes not proceed due to the residual water or protic solvent.

According to a preferred aspect, the aprotic solvent is dimethylsulfoxide, and the modifying agent is vinyl acetate or acetic anhydride.From the viewpoint of inhibiting yellowing of the chemically modifiedfine fibers or resin composite and reducing variation in chemicalmodification, the ionic liquid in the dispersion is preferably at acontent of less than 20 mass %, more preferably it is essentially absent(specifically, 1 mass % or lower), and most preferably it is completelyabsent. In addition, sulfuric acid is preferably essentially absent(specifically, 1 mass % or lower), and more preferably it is completelyabsent, in the dispersion.

The micronized (defibrated) and chemically modified microfilaments maybe prepared using an apparatus that applies impact shearing, such as aplanetary ball mill or bead mill, an apparatus that applies a rotatingshear field that induces fibrillation of cellulose, such as a discrefiner or grinder, or an apparatus that can carry out functions ofkneading, agitation and dispersion in a highly efficient manner, such asany of various types of kneaders or planetary mixers, or a rotaryhomogenizing mixer, with no limitation to these.

In the attenuated total reflection infrared absorption spectrum of thechemically modified fine fibers, the peak locations of the absorptionbands vary depending on the type of chemically modified groups. Based onvariation in the peak locations it is possible to determine on whichabsorption bands the peaks are based, allowing identification ofmodifying groups. It is also possible to calculate the modification ratefrom the peak intensity ratio of peaks attributable to the modifyinggroups and peaks attributable to the cellulose backbone.

For example, if the modifying group is an acyl group, the peak of theabsorption band for the acyl group C═O appears at 1730 cm⁻¹, the peak ofthe absorption band for cellulose backbone chain C—H groups appears at1370 cm⁻¹, and the peak of the absorption band for cellulose backbonechain C—O groups appears at 1030 cm⁻¹ (see FIG. 2).

When the chemically modified groups of the chemically modified finefibers are acyl groups, the degree of modification (modification rate)(IR index 1370), as defined by the ratio of the peak intensity of theabsorption band of the chemically modified groups (peak height ofabsorption band for acyl C═O groups) with respect to the peak intensity(height) of the absorption band for cellulose backbone chain C—H groups(peak height of absorption band for chemically modified groups/peakheight of absorption band for cellulose backbone chain C—H groups), inthe attenuated total reflection infrared absorption spectrum, ispreferably 0.28 to 1.8. If the IR index 1370 is 0.28 or greater, it willbe possible to obtain a resin composite containing chemically modifiedfine fibers with a high thermal decomposition initiation temperature. Ifit is 1.8 or lower, unmodified cellulose backbone will remain in thechemically modified fine fibers, making it possible to obtain a resincomposite containing chemically modified fine fibers which exhibits boththe high tensile strength and dimensional stability of the cellulose andthe high thermal decomposition initiation temperature due to chemicalmodification. The IR index 1370 is more preferably 0.44 or greater, evenmore preferably 0.50 or greater, yet more preferably 0.56 or greater,especially preferably 0.77 or greater and most preferably 0.87 orgreater, and more preferably 1.68 or lower, even more preferably 1.50 orlower, yet more preferably 1.31 or lower and most preferably 1.17 orlower.

The degree of modification (modification rate) (IR index 1030), asdefined by the ratio of the peak intensity of the absorption band forthe chemically modified groups (peak height of absorption band for acylC═O groups) with respect to the peak intensity (height) of theabsorption band for cellulose backbone chain C—O groups (peak height ofabsorption band for chemically modified groups/peak height of absorptionband for cellulose backbone chain C—O groups), in the attenuated totalreflection infrared absorption spectrum, is preferably 0.024 to 0.48. Ifthe IR index 1030 is 0.024 or greater, it will be possible to obtain aresin composite containing chemically modified fine fibers with a highthermal decomposition initiation temperature. If it is 0.48 or lower,unmodified cellulose backbone will remain in the chemically modifiedfine fibers, making it possible to obtain a resin composite containingchemically modified fine fibers, which exhibits both the high tensilestrength and dimensional stability of the cellulose and the high thermaldecomposition initiation temperature due to chemical modification. TheIR index 1030 is more preferably 0.048 or greater, even more preferably0.061 or greater, yet more preferably 0.073 or greater, especiallypreferably 0.13 or greater and most preferably 0.15 or greater, and morepreferably 0.44 or lower, even more preferably 0.36 or lower, yet morepreferably 0.30 or lower and most preferably 0.25 or lower.

The peak heights at 1730 cm⁻¹, 1370 cm⁻¹ and 1030 cm⁻¹ used forcalculation of the IR index 1370 and IR index 1030 are read off in thefollowing manner. For the peak intensity at 1730 cm⁻¹, a baselineconnecting locations near 1550 cm⁻¹ and near 1850 cm⁻¹ without otherpeaks is drawn with a straight line, and the height of the baseline at1730 cm⁻¹ is subtracted from the peak height at 1730 cm⁻¹ as the readvalue.

For the peak intensity at 1370 cm⁻¹, a baseline connecting locationsnear 820 cm⁻¹ and near 1530 cm⁻¹ without other peaks is drawn with astraight line, and the height of the baseline at 1370 cm⁻¹ is subtractedfrom the peak height at 1370 cm⁻¹ as the read value.

For the peak intensity at 1030 cm⁻¹, a baseline connecting locationsnear 820 cm⁻¹ and near 1530 cm⁻¹ without other peaks is drawn with astraight line, and the height of the baseline at 1030 cm⁻¹ subtractedfrom the peak height at 1030 cm⁻¹ as the read value.

The IR index 1030 can be calculated as the average degree ofsubstitution of hydroxyl groups of the chemically modified fine fibersaccording to the following formula (the average number of hydroxylgroups replaced per glucose as the basic structural unit of cellulose,also known as DS).

DS=4.13×IR Index 1030

The average degree of substitution is preferably 0.1 to 2.0. If DS is0.1 or greater, it will be possible to obtain a resin compositecontaining chemically modified fine fibers with a high thermaldecomposition initiation temperature. If it is 2.0 or lower, unmodifiedcellulose backbone will remain in the chemically modified fine fibers,making it possible to obtain a resin composite containing chemicallymodified fine fibers, which exhibits both the high tensile strength anddimensional stability of the cellulose and the high thermaldecomposition initiation temperature due to chemical modification. DS ismore preferably 0.2 or greater, more preferably 0.25 or greater, evenmore preferably 0.3 or greater and most preferably 0.5 or greater, andpreferably 1.8 or lower, more preferably 1.5 or lower, even morepreferably 1.2 or lower and most preferably 1.0 or lower.

For chemically modified fine fibers of this embodiment, the DSnon-uniformity ratio (DSs/DSt), defined as the ratio of the degree ofmodification (DSs) of the fiber surfaces with respect to the degree ofmodification (DSt) of the entire fibers, is preferably 1.05 or greater.A larger value for the DS non-uniformity ratio corresponds to a morenon-uniform structure similar to a sheath-core structure (that is, whilethe fiber surfaces are highly chemically modified, the center sectionsof the fibers maintain the original largely unmodified cellulosestructure), which helps to provide the high tensile strength anddimensional stability of cellulose while improving the affinity with theresin when used in a resin composite and improving the dimensionalstability of the resin composite. The DS non-uniformity ratio ispreferably 1.1 or greater, more preferably 1.2 or greater and even morepreferably 1.5 or greater, while from the viewpoint of ease ofproduction of the chemically modified fine fibers, it is preferably 6 orlower, more preferably 4 or lower and even more preferably 3 or lower.

The values of DSs and DSt vary depending on the degree of modificationof the chemically modified fine fibers, but for example, the preferredrange for DSs is 0.5 to 3.0 and the preferred range for DSt is 0.1 to2.0.

In the chemically modified fine fibers of this embodiment, a lowercoefficient of variation (CV) of the DS non-uniformity ratio ispreferred because it corresponds to less variation in the physicalproperties of the resin composite. It is preferably 50% or lower, morepreferably 40% or lower, even more preferably 30% or lower and mostpreferably 20% or lower. When producing the chemically modified finefibers, the coefficient of variation can be lowered by a method of firstdefibrating the cellulose starting material and then carrying out thechemical modification (sequential method). It can be increased, on theother hand, by a method of simultaneously defibrating and chemicallymodifying the cellulose starting material (simultaneous method). Whilethe action mechanism for this is not completely understood, it isbelieved that in the simultaneous method, chemical modification proceedsfurther with the narrow fibers produced by initial defibrating, and thechemical modification causes reduction in hydrogen bonding between thecellulose microfibrils, thus promoting further defibration and resultingin a larger coefficient of variation of the DS non-uniformity ratio.

The coefficient of variation (CV) of the DS non-uniformity ratio isobtained by sampling 100 g of the aqueous dispersion of the chemicallymodified fine fibers (solid content: 10 mass %), using 10 g each of thefreeze-shattered substance as measuring samples, calculating the DSnon-uniformity ratio from DSt and DSs for the 10 samples, andcalculating the coefficient of variation from the standard deviation (a)and arithmetic mean (μ) of the DS non-uniformity ratio between the 10samples.

DS Non-uniformity ratio=DSs/DSt

Coefficient of variation(%)=standard deviation σ/arithmetic mean μ×100

The method of calculating DSt may be subjecting the freeze-shatteredchemically modified fine fibers to ¹³C solid NMR measurement, accordingto the following formula using the area intensity (Inf) of the signalattributed to one carbon atom of the modifying group, with respect tothe total area intensity (Inp) of the signals attributed to C1-C6carbons of the pyranose rings of cellulose, appearing in the range of 50ppm to 110 ppm.

DSt=(Inf)×6/(Inp)

For example, when the modifying group is acetyl, the signal at 23 ppmattributed to —CH₃ may be used.

The conditions in the ¹³C solid NMR measurement may be as follows, forexample.

Apparatus: Bruker Biospin Avance 500WB Frequency: 125.77 MHz

Measuring method: DD/MASLatency time: 75 secNMR sample tube:4 mmφNumber of scans: 640 (˜14 hr)

MAS: 14,500 Hz

Chemical shift reference: glycine (external reference: 176.03 ppm)

As the method of calculating DSs, a powder sample of the chemicallymodified fine fibers used for ¹³C solid NMR measurement is placed on a2.5 mmφ dish-shaped sample stand, the surface is pressed flat, andmeasurement is performed by X-ray photoelectron spectroscopy (XPS). TheXPS spectrum reflects the structural elements and chemically bondedstate of the sample surface layer alone (typically about severalnanometers). The obtained Cls spectrum is analyzed by peak separation,and calculation is performed by the following formula using the areaintensity (Ixf) of the peak attributed to one carbon atom of themodifying group, with respect to the area intensity (Ixp) of the peakattributed to the C2-C6 carbons of the pyranose rings of cellulose (289eV, C—C bond).

DSs=(Ixf)×5/(Ixp)

For example, when the modifying group is acetyl, the Cls spectrum isanalyzed by peak separation at 285 eV, 286 eV, 288 eV and 289 eV, andthe peak at 289 eV may be used for Ixp while the peak due to acetylgroup O—C═O bonds (286 eV) may be used for Ixf.

The conditions for XPS measurement are the following, for example.

Device: VersaProbe II by Ulvac-Phi, Inc.

Excitation source: mono. AlKa 15 kV×3.33 mAAnalysis size: ˜200 μmφPhotoelectron take-off angle: 45°Capture rangeNarrow scan: C 1s, O 1s

Pass Energy: 23.5 eV

For a resin composite according to a typical aspect, the resin forms amatrix, with the chemically modified fine fibers dispersed in the resin.

According to one aspect, the resin composite can be produced by aproduction method comprising a step of defibrating cellulose in adispersion containing a cellulose starting material at a purity of 85mass % or greater, and an aprotic solvent, to obtain fine cellulosefibers, and then adding a solution containing a modifying agent to thedispersion to modify the fine cellulose fibers, thereby obtainingchemically modified fine fibers having a thermal decompositioninitiation temperature (T_(D)) of 270° C. or higher, a number-averagefiber diameter of 10 nm or greater and less than 1 μm (and with a degreeof crystallinity of 60% or higher, according to one aspect), and a stepof mixing the chemically modified fine fibers with a resin. Thus, themethod of chemical modification after preparation of fine cellulosefibers by defibrating is advantageous from the viewpoint of lowering thecoefficient of variation of the DS non-uniformity ratio (DSs/DSt). Fromthe viewpoint of inhibiting yellowing of the chemically modified finefibers or resin composite and reducing variation in chemicalmodification, the ionic liquid in the dispersion is preferably at acontent of less than 20 mass %, more preferably it is essentially absent(specifically, 1 mass % or lower), and most preferably it is completelyabsent. In addition, sulfuric acid is preferably essentially absent(specifically, 1 mass % or lower), and more preferably it is completelyabsent, in the dispersion.

Using a cellulose starting material with a purity (α-cellulose content)of 85 mass % or greater, as the starting material for the type Icellulose crystals, is preferred from the viewpoint of the productionefficiency and refining efficiency of the chemically modified finefibers (that is, the purity of the chemically modified fine fibers), andthe physical properties when composited with a resin. The cellulosepurity is more preferably 90 mass % or greater and even more preferably95 mass % or greater.

The cellulose purity can be determined by a method for measuringα-cellulose content described in non-patent literature (MokushitsuKagaku Jikken Manual, ed. The Japan Wood Research Society, pp. 92-97,2000).

The starting material for the type II cellulose crystals may exhibit alow cellulose purity when using a method of measuring the α-cellulosecontent (the α-cellulose content measuring method is a method originallydeveloped for analysis of type I cellulose crystal starting materialssuch as wood). However, a starting material for type II cellulosecrystals is a product processed and produced using type I cellulosecrystals as starting material (such as viscose rayon, cupra, lyocell ormercerized cellulose), the original cellulose purity is high. The typeII cellulose crystal starting material is therefore suitable as astarting material for the chemically modified fine fibers of theinvention even with a cellulose purity of less than 85 mass %.

The resin composite may also include cellulose whiskers in addition tothe chemically modified fine fibers. Cellulose whiskers improve thedispersibility of the chemically modified fine fibers by admixture withthe chemically modified fine fibers, resulting in improved dynamicproperties of the resin composite. The major property of cellulosewhiskers is L/D=1 to <30, preferably L/D=1 to 20 and more preferablyL/D=1 to 10, without being limited to this range. The degree ofcrystallinity of the cellulose whiskers is 70% or higher, for example,and is preferably 80% or higher. The degree of polymerization of thecellulose whiskers is 600 or lower and preferably 300 or lower. Thecellulose whiskers used may be a commercially available product, and forexample, it may be obtained by cutting wood pulp and promotinghydrolysis in an aqueous hydrochloric acid solution.

Using a dispersion stabilizer that has the function of stably dispersingthe chemically modified fine fibers, together with the chemicallymodified fine fibers, to increase and control the dispersed state of thechemically modified fine fibers in the resin, is effective for improvingthe mechanical properties of the resin composite. The content ratio ofthe dispersion stabilizer in the resin composite is appropriatelyselected in a range that does not interfere with the desired effect ofthe invention, and for example, it may be 0.01 to 50 mass %, 0.1 to 30mass %, 0.5 to 20 mass % or 1.0 to 10 mass %.

According to a more preferred aspect, the chemically modified finefibers are dispersed in the resin composite in the form of a cellulosedispersion containing a dispersion stabilizer. The chemically modifiedfine fiber content in the cellulose dispersion is preferably 10 to 99mass %, more preferably 10 to 90 mass % and even more preferably 50 to90 mass %. When the chemically modified fine fiber content is higher,the dispersion of the chemically modified fine fibers is poor and themechanical properties are insufficiently improved, and when it is lower,the dispersion stabilizer causes the resin to become too sparse,resulting in poor mechanical properties. A portion of the dispersionstabilizer may elute from the cellulose dispersion during production ofthe resin composite, and may diffuse in the matrix resin in the resincomposite.

The dispersion stabilizer may be one or more selected from the groupconsisting of surfactants, organic compounds with boiling points of 160°C. or higher, and resins having chemical structures that are able tohighly disperse the chemically modified fine fibers, and preferably oneor more selected from the group consisting of surfactants and organiccompounds with boiling points of 160° C. or higher.

The surfactant may be one having a chemical structure in which a sitewith a hydrophilic substituent and a site with a hydrophobic substituentare covalently bonded, and any ones utilized for a variety of purposesincluding consumption and industrial use may be used. The following, forexample, may be used, either alone or in combinations of two or more.

The surfactant used may be any anionic surfactant, nonionic surfactant,zwitterionic surfactant or cationic surfactant, but from the viewpointof affinity with cellulose, an anionic surfactant or nonionic surfactantis preferred, and a nonionic surfactant is more preferred.

Among the above, from the viewpoint of affinity with cellulose,surfactants having polyoxyethylene chains, carboxyl groups or hydroxylgroups as hydrophilic groups are preferred, polyoxyethylene-basedsurfactants with polyoxyethylene chains as hydrophilic groups(polyoxyethylene derivatives) are more preferred, and nonionicpolyoxyethylene derivatives are even more preferred. The polyoxyethylenechain length of a polyoxyethylene derivative is preferably 3 or greater,more preferably 5 or greater, even more preferably 10 or greater andmost preferably 15 or greater. A longer chain length will increase theaffinity with cellulose, but for balance with the properties desired forthe resin composite (for example, the coating property), it ispreferably no greater than 60, as the upper limit, more preferably nogreater than 50, even more preferably no greater than 40, especiallypreferably no greater than 30 and most preferably no greater than 20.

Of the aforementioned surfactants, it is especially preferred to usethose with alkyl ether-type, alkylphenyl ether-type, rosin ester-type,bisphenol A-type, β-naphthyl-type, styrenated phenyl-type orhydrogenated castor oil-type hydrophobic groups, because of their highaffinity with resins. The alkyl chain length (the number of carbon atomsexcluding the phenyl group in the case of alkylphenyl) is a carbon chainof preferably 5 or greater, more preferably 10 or greater, even morepreferably 12 or greater and most preferably 16 or greater carbon atoms.When the resin is a polyolefin-based resin, for example, a greaternumber of carbon atoms of the surfactant increases affinity with theresin, and therefore while there is no strict upper limit, the upperlimit for the number of carbon atoms is preferably no more than 30 andmore preferably no more than 25.

Preferred among these hydrophobic groups are those having a cyclicstructure and those having bulk and a polyfunctional structure. Thosewith a cyclic structure include alkylphenyl ether-type, rosinester-type, bisphenol A-type, β-naphthyl-type and styrenated phenyl-typegroups, and those with a polyfunctional structure include hydrogenatedcastor oil-type groups.

More particularly preferred among these are rosin ester types andhydrogenated castor oil types.

Organic compounds with boiling points of 160° C. or higher are effectiveas non-surfactant dispersing media, although this will depend on thetype of resin. Specific examples of such organic compounds that areeffective include high-boiling-point organic solvents such as liquidparaffin and decalin, when the resin is a polyolefin-based resin. Whenthe resin is a polar resin such as a polyamide-based resin orpolyacetate-based resin, it is effective to use the same solvent as theaprotic solvent that may be used for production of the chemicallymodified fine fibers, such as dimethyl sulfoxide, for example.

The resin composite of this embodiment may also include othercomponents, namely additives including fine fiber filler componentscomposed of highly heat-resistant organic polymers other than chemicallymodified fine fibers (for example, fibrillated fibers fine fibersobtained from aramid fibers); compatibilizers; plasticizers;polysaccharides such as starch and alginic acid; natural proteins suchas gelatin, nikawa and casein; inorganic compounds such as zeolite,ceramics, talc, silica, metal oxides and metal powders; coloring agents;perfumes; pigments; flow adjusters; leveling agents; conductive agents;antistatic agents; ultraviolet absorbers; ultraviolet dispersing agents;and deodorants. The content ratio of optional additives in the resincomposite is appropriately selected in a range that does not interferewith the desired effect of the invention, and for example, it may be0.01 to 50 mass % or 0.1 to 30 mass %.

With chemically modified fine fibers in the resin composite, aggregationby hydrogen bonding will be reduced compared to unmodified finecellulose fibers. Thus, in the mixing step for the chemically modifiedfine fibers and resin, aggregation between chemically modified finefibers is minimized, the chemically modified fine fibers homogeneouslydisperse in the resin, and a fiber-reinforced resin complex containingchemically modified fine fibers can be obtained that has excellentdynamic properties, heat resistance, surface smoothness and outerappearance.

The resin composite containing chemically modified fine fibers accordingto this embodiment has a satisfactory balance for its mechanicalproperties, including its static properties in bending testing anddynamic properties in impact testing.

The resin used in the resin composite of this embodiment may be athermoplastic resin, a thermosetting resin and/or a photocuring resin.The resin may also be an elastomer.

The content of the resin (matrix resin) in the resin composite may be 60to 99.5 mass %, and more preferably 80 to 90 mass %. A resin content of60 mass % or greater is effective for exhibiting thermal stability(lower linear coefficient of thermal expansion, and retaining elasticityat high temperature), while a resin content of 99.5 mass % or lower willallow functions such as a high elastic modulus and lower coefficient ofthermal expansion to be imparted to the resin composite.

When the resin is a thermoplastic resin, the melting point of thethermoplastic resin may be appropriately selected depending on thepurpose of use of the resin composite. For a resin with a relatively lowmelting point (such as a polyolefin-based resin), for example, themelting point of the thermoplastic resin may be 150° C. to 190° C. or160° C. to 180° C., while for a resin with a relatively high meltingpoint (such as a polyamide-based resin), for example, it may be 220° C.to 350° C. or 230° C. to 320° C.

The thermoplastic resin may be at least one type selected from the groupconsisting of polyolefin-based resins, polyacetate-based resins,polycarbonate-based resins, polyamide-based resins, polyester-basedresins, polyphenylene ether-based resins and acrylic-based resins.

Polyolefin-based resins that are preferred as thermoplastic resins arepolymers obtained by polymerizing olefins (such as α-olefins) and/oralkenes as monomer units. Specific examples of polyolefin-based resinsinclude ethylene-based (co)polymers such as low-density polyethylene(for example, linear low-density polyethylene), high-densitypolyethylene, ultralow-density polyethylene and ultrahigh molecularweight polyethylene, polypropylene-based (co)polymers such aspolypropylene, ethylene-propylene copolymer and ethylene-propylene-dienecopolymer, and copolymers with α-olefins such as ethylene, includingethylene-acrylic acid copolymer, ethylene-methyl methacrylate copolymerand ethylene-glycidyl methacrylate copolymer.

The most preferred polyolefin-based resin is polypropylene. Particularlypreferred is polypropylene, which has a melt mass-flow rate (MFR) of 3g/10 min to 30 g/10 min, as measured at 230° C. with a load of 21.2 N,according to ISO1133. The lower limit for MFR is more preferably 5 g/10min, even more preferably 6 g/10 min and most preferably 8 g/10 min. Theupper limit for MFR is more preferably 25 g/10 min, even more preferably20 g/10 min and most preferably 18 g/10 min. The MFR preferably is notabove this upper limit from the viewpoint of increased toughness of thecomposition, and it is preferably not less than the lower limit from theviewpoint of the flow property of the composition.

An acid-modified polyolefin-based resin may also be suitably used inorder to increase the affinity with cellulose. The acid may beappropriately selected from among maleic acid, fumaric acid, succinicacid, phthalic acid and their anhydrides, and polycarboxylic acids suchas citric acid. Preferred among these are maleic acid or its anhydride,for an increased modification rate. While the modification method is notparticularly restricted, a common method involves heating to above themelting point in the presence of or in the absence of a peroxide, formelt kneading. The polyolefin resin to be acid-modified may be any ofthe aforementioned polyolefin-based resins, but polypropylene is mostsuitable for use. The acid-modified polypropylene may be used alone, butit is preferably used in admixture with a non-modified polypropylene inorder to adjust the modification rate of the entire resin. Theproportion of acid-modified polypropylene with respect to the totalpolypropylene is 0.5 mass % to 50 mass %. The lower limit is morepreferably 1 mass %, even more preferably 2 mass %, yet more preferably3 mass %, even yet more preferably 4 mass % and most preferably 5 mass%. The upper limit is more preferably 45 mass %, even more preferably 40mass %, yet more preferably 35 mass %, even yet more preferably 30 mass% and most preferably 20 mass %. In order to maintain interfacialstrength between the resin and the cellulose it is preferably higherthan the lower limit, and in order to maintain ductility as a resin itis preferably lower than the upper limit.

The melt mass-flow rate (MFR) of the acid-modified polypropylene asmeasured at 230° C. with a load of 21.2 N according to ISO1133 ispreferably 50 g/10 min or higher, in order to increase affinity with thecellulose interface. A more preferred lower limit is 100 g/10 min, with150 g/10 min being more preferred and 200 g/10 min being most preferred.There is no particular upper limit, and it may be 500 g/10 min in orderto maintain mechanical strength. An MFR within this range will providean advantage of residing more easily at the interface between thecellulose and the resin.

Examples of preferred polyamide-based resins for the thermoplastic resininclude polyamides obtained by polycondensation reaction of lactams(such as polyamide 6, polyamide 11 and polyamide 12), and polyamidesobtained by copolymerization of diamines (such as 1,6-hexanediamine,2-methyl-1,5-pentanediamine, 1,7-heptanediamine,2-methyl-1-6-hexanediamine, 1,8-octanediamine,2-methyl-1,7-heptanediamine, 1,9-nonanediamine,2-methyl-1,8-octanediamine, 1,10-decanediamine, 1,11-undecanediamine,1,12-dodecanediamine and m-xylylenediamine) and dicarboxylic acids (suchas butanedioic acid, pentanedioic acid, hexanedioic acid, heptanedioicacid, octanedioic acid, nonanedioic acid, decanedioic acid,benzene-1,2-dicarboxylic acid, benzene-1,3-dicarboxylic acid,benzene-1,4-dicarboxylic acid, cyclohexane-1,3-dicarboxylic acid andcyclohexane-1,4-dicarboxylic acid) (such as polyamide 6,6, polyamide6,10, polyamide 6,11, polyamide 6,12, polyamide 6,T, polyamide 6,1,polyamide 9,T, polyamide 10,T, polyamide 2M5,T, polyamide MXD, 6,polyamide 6,C and polyamide 2M5,C), as well as copolymers obtained bycopolymerization of these (such as polyamide 6,T/6,I).

More preferred among these polyamide-based resins are aliphaticpolyamides such as polyamide 6, polyamide 11, polyamide 12, polyamide6,6, polyamide 6,10, polyamide 6,11 and polyamide 6,12, and alicyclicpolyamides such as polyamide 6,C and polyamide 2M5,C.

For increased heat resistance of the resin composite, the melting pointof the polyamide-based resin is preferably 220° C. or higher, morepreferably 230° C. or higher, even more preferably 240° C. or higher,yet more preferably 245° C. or higher and most preferably 250° C. orhigher, while from the viewpoint of easier production of the resincomposite, the melting point is preferably no higher than 350° C., nohigher than 320° C. or no higher than 300° C.

There are no particular restrictions on the terminal carboxyl groupconcentration of the polyamide-based resin, but the lower limit ispreferably 20 μmol/g and more preferably 30 μmol/g. The upper limit forthe terminal carboxyl group concentration is preferably 150 μmol/g, morepreferably 100 μmol/g and even more preferably 80 μmol/g.

In the polyamide-based resin, the ratio of carboxyl terminal groups withrespect to the total terminal groups ([COOH]/[total terminal groups]) ismore preferably 0.30 to 0.95. The lower limit for the carboxyl terminalgroup ratio is more preferably 0.35, yet more preferably 0.40 and mostpreferably 0.45. The upper limit for the carboxyl terminal group ratiois more preferably 0.90, yet more preferably 0.85 and most preferably0.80. The carboxyl terminal group ratio is preferably 0.30 or higherfrom the viewpoint of dispersibility of the chemically modified finefibers in the resin composite, and preferably 0.95 or lower from theviewpoint of the color tone of the resulting resin composite.

The method used to adjust the terminal group concentration of thepolyamide-based resin may be a publicly known method. For example, themethod may be addition of a terminal group adjuster that reacts with theterminal groups, such as a diamine compound, monoamine compound,dicarboxylic acid compound, monocarboxylic acid compound, acidanhydride, monoisocyanate, monoacid halide, monoester or monoalcohol, tothe polymerization solution, so as to result in the prescribed terminalgroup concentration during polymerization of the polyamide.

Examples of terminal group adjusters that react with terminal aminogroups include aliphatic monocarboxylic acids such as acetic acid,propionic acid, butyric acid, valeric acid, caproic acid, caprylic acid,lauric acid, tridecanoic acid, myristic acid, palmitic acid, stearicacid, pivalic acid and isobutyric acid; alicyclic monocarboxylic acidssuch as cyclohexanecarboxylic acid; aromatic monocarboxylic acids suchas benzoic acid, toluic acid, α-naphthalenecarboxylic acid,β-naphthalenecarboxylic acid, methylnaphthalenecarboxylic acid andphenylacetic acid; and mixtures of any selected from among theforegoing. Among these, from the viewpoint of reactivity, stability ofcapped ends and cost, one or more terminal group adjusters selected fromthe group consisting of acetic acid, propionic acid, butyric acid,valeric acid, caproic acid, caprylic acid, lauric acid, tridecanoicacid, myristic acid, palmitic acid, stearic acid and benzoic acid arepreferred, with acetic acid being most preferred.

Examples of terminal group adjusters that react with terminal carboxylgroups include aliphatic monoamines such as methylamine, ethylamine,propylamine, butylamine, hexylamine, octylamine, decylamine,stearylamine, dimethylamine, diethylamine, dipropylamine anddibutylamine; alicyclic monoamines such as cyclohexylamine anddicyclohexylamine; aromatic monoamines such as aniline, toluidine,diphenylamine and naphthylamine; and any mixtures of the foregoing.Among these, from the viewpoint of reactivity, boiling point, capped endstability and cost, it is preferred to use one or more terminal groupadjusters selected from the group consisting of butylamine, hexylamine,octylamine, decylamine, stearylamine, cyclohexylamine and aniline.

The concentration of the amino terminal groups and carboxyl terminalgroups is preferably determined from the integral of the characteristicsignal corresponding to each terminal group, according to ¹H-NMR, fromthe viewpoint of precision and convenience. The recommended method fordetermining the terminal group concentration is, specifically, themethod described in Japanese Unexamined Patent Publication HEI No.7-228775. When this method is used, heavy trifluoroacetic acid is usefulas the measuring solvent. Also, the number of scans in ¹H-NMR must be atleast 300, even with measurement using a device having sufficientresolving power. Alternatively, the terminal group concentration can bemeasured by a titration method such as described in Japanese UnexaminedPatent Publication No. 2003-055549. However, in order to minimize theeffects of the mixed additives and lubricant, quantitation is preferablyby ¹H-NMR.

The intrinsic viscosity [₁] of the polyamide-based resin, measured inconcentrated sulfuric acid at 30° C., is preferably 0.6 to 2.0 dL/g,more preferably 0.7 to 1.4 dL/g, even more preferably 0.7 to 1.2 dL/gand most preferably 0.7 to 1.0 dL/g. If the aforementioned polyamidehaving intrinsic viscosity in the preferred range, or the particularlypreferred range, is used, it will be possible to provide an effect ofdrastically increasing the flow property of the resin composite in thedie during injection molding, and improving the outer appearance ofmolded pieces.

Throughout the present disclosure, “intrinsic viscosity” is synonymouswith the viscosity commonly known as the limiting viscosity. Thespecific method for determining the viscosity is a method in which theηsp/c of several measuring solvents with different concentrations ismeasured in 96% concentrated sulfuric acid under temperature conditionsof 30° C., the relational expression between each ηsp/c and theconcentration (c) is derived, and the concentration is extrapolated tozero. The value extrapolated to zero is the intrinsic viscosity.

The details are described in Polymer Process Engineering (Prentice-Hall,Inc 1994), p. 291-294.

The number of measuring solvents with different concentrations ispreferably at least 4, from the viewpoint of precision. Theconcentrations of the recommended measuring solutions with differentviscosities are preferably at least four: 0.05 g/dL, 0.1 g/dL, 0.2 g/dLand 0.4 g/dL.

Polyester-based resins that are preferred as thermoplastic resins areone or more selected from among polyethylene terephthalate (hereunderalso referred to simply as “PET”), polybutylene succinate (a polyesterresin composed of an aliphatic polybasic carboxylic acid and analiphatic polyol (hereunder also referred to simply as “unit PBS”)),polybutylene succinate adipate (hereunder also referred to simply as“PBSA”), polybutylene adipate terephthalate (hereunder also referred tosimply as “PBAT”), polyhydroxyalkanoic acids (polyester resins composedof 3-hydroxyalkanoic acids, hereunder also referred to simply as “PHA”),polylactic acid (hereunder also referred to simply as “PLA”),polybutylene terephthalate (hereunder also referred to simply as “PBT”),polyethylene naphthalate (hereunder also referred to simply as “PEN”)and polyallylates (hereunder also referred to simply as “PAR”).

Preferred polyester-based resins among these include PET, PBS, PBSA, PBTand PEN, with PBS, PBSA and PBT being more preferred.

The terminal groups of the polyester-based resin can be freely alteredby the monomer ratio during polymerization and/or by the presence orabsence and amount of stabilizer at the ends, and more preferably theratio of carboxyl terminal groups with respect to the total terminalgroups of the polyester-based resin ([C001-1]/[total terminal groups])is 0.30 to 0.95. The lower limit for the carboxyl terminal group ratiois more preferably 0.35, yet more preferably 0.40 and most preferably0.45. The upper limit for the carboxyl terminal group ratio is morepreferably 0.90, yet more preferably 0.85 and most preferably 0.80. Thecarboxyl terminal group ratio is preferably 0.30 or greater from theviewpoint of dispersibility of the microcellulose in the composition,and it is preferably no greater than 0.95 from the viewpoint of thecolor tone of the obtained composition.

Polyacetal-based resins preferred as thermoplastic resins are commonlyhomopolyacetals obtained from formaldehyde starting materials andcopolyacetals with trioxane as the main monomer and comprising1,3-dioxolane as a comonomer component, and although both of these maybe used, copolyacetals are preferably used from the viewpoint of thermalstability during working. The percentage of structure due to thecomonomer component (for example, 1,3-dioxolane) is more preferably inthe range of 0.01 to 4 mol %. The preferred lower limit for thepercentage of structure due to the comonomer component is 0.05 mol %,more preferably 0.1 mol % and even more preferably 0.2 mol %. Thepreferred upper limit is 3.5 mol %, more preferably 3.0 mol %, even morepreferably 2.5 mol % and most preferably 2.3 mol %. The lower limit ispreferably in the range specified above from the viewpoint of thermalstability during extrusion and during molding, and the upper limit ispreferably in the range specified above from the viewpoint of mechanicalstrength.

Specific examples of thermosetting resins include, but are notparticularly limited to, bisphenol-type epoxy resins such as bisphenolA-type epoxy resin, bisphenol F-type epoxy resin, bisphenol S-type epoxyresin, bisphenol E-type epoxy resin, bisphenol M-type epoxy resin,bisphenol P-type epoxy resin and bisphenol Z-type epoxy resin,novolac-type epoxy resins such as bisphenol A-novolac-type epoxy resin,phenol-novolac-type epoxy resin and cresol-novolac-epoxy resin,biphenyl-type epoxy resins, biphenylaralkyl-type epoxy resins,arylalkylene-type epoxy resins, tetraphenylolethane-type epoxy resins,naphthalene-type epoxy resins, anthracene-type epoxy resins,phenoxy-type epoxy resins, dicyclopentadiene-type epoxy resins,norbornane-type epoxy resins, adamantane-type epoxy resins,fluorene-type epoxy resins, glycidyl methacrylate copolymer-based epoxyresins, cyclohexylmaleimide and glycidyl methacrylate copolymer epoxyresins, epoxy-modified polybutadiene rubber derivatives, CTBN-modifiedepoxy resins, trimethylolpropane polyglycidyl ether,phenyl-1,3-diglycidyl ether, biphenyl-4,4′-diglycidyl ether,1,6-hexanediol diglycidyl ether, diglycidyl ethers of ethylene glycol orpropylene glycol, sorbitol polyglycidyl ether, tris(2,3-epoxypropyl)isocyanurate, triglycidyltris(2-hydroxyethyl) isocyanurate, phenolresins, including novolac-type phenol resins such as phenol-novolacresin, cresol-novolac resin and bisphenol A-novolac resin, resol-typephenol resins such as modified resol phenol resins, oil-modified resolphenol resins modified with China wood oil, linseed oil or walnut oil,phenoxy resins, urea resins, triazine ring-containing resins such asmelamine resins, unsaturated polyester resins, bismaleimide resins,diallyl phthalate resins, silicone resins, benzoxazine ring-containingresins, norbornane-based resins, cyanate resins, isocyanate resins,urethane resins, benzocyclobutene resins, maleimide resins,bismaleimidetriazine resins, polyazomethine resins, and thermosettingpolyimides.

These thermosetting resins may be used alone, or two or more differenttypes may be used as blends. For a blend, the blend ratio may beappropriately set depending on the particular use.

Specific examples of photocuring resins include, but are notparticularly limited to, common publicly known (meth)acrylate resins,vinyl resins and epoxy resins. These are largely classified depending onthe reaction mechanism, either as radical reactive types wherein amonomer reacts by radicals generated from light, or cation reactivetypes wherein a monomer undergoes cationic polymerization. Radicalreactive monomers include (meth)acrylate compounds and vinyl compounds(such as certain types of vinyl ethers). Cation reactive types includeepoxy compounds, and certain types of vinyl ethers. For example, anepoxy compound that can be used as a cation reactive type can serve as amonomer for both thermosetting resins and photocuring resins.

A (meth)acrylate compound is a compound having at least one(meth)acrylate group in the molecule. Specific examples of(meth)acrylate compounds include monofunctional (meth)acrylates,polyfunctional (meth)acrylates, epoxy acrylates, polyester acrylates,and urethane acrylates.

Vinyl compounds include vinyl ethers, styrene and styrene derivatives,and vinyl compounds. Vinyl ethers include ethylvinyl ether, propylvinylether, hydroxyethylvinyl ether and ethyleneglycol divinyl ether. Styrenederivatives include methylstyrene and ethylstyrene. Vinyl compoundsinclude triallyl isocyanurate and trimethallyl isocyanurate.

Reactive oligomers may also be used as photocuring resin startingmaterials. Reactive oligomers include oligomers having any combinationselected from among (meth)acrylate groups, epoxy groups, urethane bondsand ester bonds in the same molecule, examples of which are a urethaneacrylate having a (meth)acrylate group and urethane bond in the samemolecule, a polyester acrylate having a (meth)acrylate group and anester bond in the same molecule, and an epoxy acrylate derived from anepoxy resin and having an epoxy group and a (meth)acrylate group in thesame molecule.

These photocuring resins may be used alone, or two or more differenttypes may be used as blends. For a blend, the blend ratio may beappropriately set depending on the particular use.

[Elastomer (Rubber)]

Specific examples of elastomers (rubbers) include, but are notparticularly limited to, natural rubber (NR), butadiene rubber (BR),styrene-butadiene copolymer rubber (SBR), isoprene rubber (IR), butylrubber (IIR), acrylonitrile-butadiene rubber (NBR),acrylonitrile-styrene-butadiene copolymer rubber, chloroprene rubber,styrene-isoprene copolymer rubber, styrene-isoprene-butadiene copolymerrubber, isoprene-butadiene copolymer rubber, chlorosulfonatedpolyethylene rubber, modified natural rubber (such as epoxidated naturalrubber (ENR), natural hydride rubber and deproteinized natural rubber),ethylene-propylene copolymer rubber, acrylic rubber, epichlorohydrinrubber, polysulfide rubber, silicone rubber, fluorine rubber andurethane rubber. These rubber materials may be used alone, or two ormore different types may be used as blends. For a blend, the blend ratiomay be appropriately set depending on the particular use.

The resin composite of this embodiment can be produced by mixing thechemically modified fine fibers with a base resin, and carrying outheat-fusion kneading, thermosetting, photocuring and curing. A moldedarticle may also be fabricated by casting the resin composite. The formin which the chemically modified fine fibers are added during productionof the resin composite is not particularly restricted, and it may be asa slurry containing not only the dry powder but also water.Water-containing slurry can be prepared by a method of halting dryingduring the drying procedure in the method for producing the chemicallymodified fine fibers, or a method of adding water after first drying.

According to one aspect, the method for producing a resin composite whenthe resin is a thermoplastic resin includes a step of kneading thechemically modified fine fibers in the form of dry powder or an aqueousdispersion inside a melt kneading molding machine, together with thethermoplastic resin, and then casting the kneaded mixture.

According to another aspect, the method for producing the resincomposite when the resin is a thermosetting resin or photocuring resinincludes a step of mixing the chemically modified fine fibers and athermosetting resin and then casting the mixture and subjecting it tothermosetting treatment, or a step of mixing the chemically modifiedfine fibers and a photocuring resin and then casting the mixture andsubjecting it to photocuring treatment.

According to yet another aspect, the method for producing the resincomposite when the resin is an elastomer includes a step of mixing thechemically modified fine fibers with a rubber starting material and thencasting the mixture and subsequently vulcanizing it. The method ofmixing the chemically modified fine fibers and the rubber startingmaterial may be a method of kneading with a kneader such as a benchroll, Banbury mixer, kneader or planetary mixer; a method of mixing witha stirring blade; or a method of mixing with a revolving or rotatingstirrer.

More specific methods for producing the resin composite when the resinis a thermoplastic resin include, but are not limited to:

1. A method of using a single-screw or twin-screw extruder for meltkneading of a mixture of the chemically modified fine fibers (dry powderor aqueous dispersion) and a thermoplastic resin, followed by:

(1) extrusion into a strand form and cooling solidification in a waterbath to obtain molded pellets of the resin composite,

(2) extrusion and cooling into a rod or tubular form to obtain anextruded body of the resin composite, or

(3) extrusion with a T-die to obtain a molded sheet or film of the resincomposite, or

2. A method of mixing the chemically modified fine fibers (dry powder oraqueous dispersion) with a thermoplastic resin monomer and conductingpolymerization reaction (specifically, solid-phase polymerization,emulsion polymerization, suspension polymerization, solutionpolymerization or bulk polymerization), and extruding the obtainedproduct by the method of any one of (1) to (3) above, to obtain a moldedresin composite.

When the resin is a thermoplastic resin, the minimum processingtemperature recommended by the supplier of the thermoplastic resin is255 to 270° C. for polyamide 66, 225 to 240° C. for polyamide 6, 170° C.to 190° C. for a polyacetal resin and 160 to 180° C. for polypropylene.The heating preset temperature is preferably in a range of 20° C. higherthan the recommended minimum processing temperature. Setting the mixingtemperature to within this range will allow the chemically modified finefibers and the resin to be uniformly mixed.

The moisture content of the resin composite is not particularlyrestricted, but for a polyamide, for example, it is preferably 10 ppm orgreater to inhibit increase in molecular weight of the polyamide duringmelting, while it is also preferably 1200 ppm or lower, more preferably900 ppm or lower and most preferably 700 ppm or lower to inhibithydrolysis of the polyamide during melting. The moisture content is thevalue measured using a Karl Fischer moisture meter by the method of ISO15512.

A resin composite with a thermoplastic resin as the resin can beutilized for various types of molded resins. The method for producingthe molded resin is not particularly restricted and any productionmethod may be employed, but the molded resin can be produced in the formof a sheet, film or fibers by injection molding (injection compressionmolding, injection press molding or gas assist injection molding), aswell as by various types of extrusion (cold runner method or hot runnermethod), foam molding (including methods involving injection ofsupercritical fluids), insert molding, in-mold coating molding,insulated die molding, rapid-heating/cooling die molding, profileextrusion methods (two-color molding, sandwich molding, and injectionmolding such as ultra high-speed injection molding), or various types ofextrusion molding methods. Inflation methods, calender methods andcasting methods may also be used for molding into a sheet or film.Molding into a heat contracted tube is also possible by using a specificstretching operation. Blow molding products can also be obtained byrotational molding or blow molding. Injection molding is most preferredamong these from the viewpoint of design and cost.

The resin composite of this embodiment may be provided in a variety ofdifferent forms. Specifically, resin pellets, sheet forms, fibrousforms, tabular forms and rod forms may be mentioned. Resin pellets aremore preferred among these for easier post-processing and facilitatedtransport. Preferred pellet forms are round, elliptical or circularcolumnar. The form of the pellets can be varied by the cutting methodused during extrusion. Pellets cut by the method known as “underwatercutting” are usually round, pellets cut by the method known as “hotcutting” are usually round or elliptical, and pellets cut by the methodknown as “strand cutting” are usually cylindrical. The preferred sizefor round pellets is 1 mm to 3 mm, as the diameter of the pellets. Thepreferred diameter for cylindrical pellets is 1 mm to 3 mm, and thepreferred length is 2 mm to 10 mm. The diameter and length arepreferably above these specified lower limits from the viewpoint ofoperational stability during extrusion, and they are preferably lowerthan the specified upper limits from the viewpoint of seizing in themolding machine in post-working.

The method for producing a resin composite when the resin is athermosetting resin or photocuring resin is not particularly restricted,and examples include methods of adequately dispersing the chemicallymodified fine fibers in a resin solution or resin powder dispersion anddrying them, methods of adequately dispersing the chemically modifiedfine fibers in a resin monomer solution and polymerizing them with heat,UV irradiation or a polymerization initiator, methods of adequatelyimpregnating a molded article (such as a sheet or molded particlepowder) of the chemically modified fine fibers with a resin solution orresin powder dispersion and drying it, and methods of adequatelyimpregnating a molded article of the chemically modified fine fiberswith a resin monomer solution and polymerizing it with heat, UVirradiation or a polymerization initiator. Any of various polymerizationinitiators, curing agents, curing accelerators and polymerizationinhibitors may be added during curing.

A resin composite with a thermosetting resin or photocuring resin as theresin can be utilized for various types of molded resins. The method ofproducing the molded resin is not particularly restricted, and any ofvarious production methods may be used.

In the case of a thermosetting resin, extrusion molding is commonly usedfor production of tabular products, but flat pressing may also beemployed. A profile extrusion method, blow molding method, compressionmolding method, vacuum forming method or injection molding may also beused. Melt extrusion or solution casting methods may be used forproduction of a film-like product, and when a melt method is used, itmay be inflation film molding, cast molding, extrusion laminationmolding, calender molding, sheet forming, fiber molding, blow molding,injection molding, rotational molding or cover molding.

After fabricating a sheet, known as the uncured or semi-cured prepreg,the prepreg may be used as a single layer or laminated, and pressed andheated for curing and molding of the resin. Methods of applying heat andpressure include press molding, autoclave molding, bagging molding,wrapping tape and internal pressure molding methods, with no limitationto these molding methods.

Methods of impregnating filaments or a preform of reinforcing fiberssuch as carbon fibers with the resin composite before resin curing, andthen curing the resin to obtain a molded article (such as RTM, VaRTM,filament winding, RFI or similar molding methods) may also be used.

When the resin is a photocuring resin, the molded article may beproduced using any of various curing methods that make use of an activeenergy beam.

The method of producing the resin composite when the resin is anelastomer, is not particularly restricted, and examples include a methodof dry kneading the chemically modified fine fibers and rubber startingmaterial, and a method of dispersing or dissolving the chemicallymodified fine fibers and rubber starting material in a dispersing mediumand then drying and kneading. The mixing method used is preferably oneusing a homogenizer, from the viewpoint of applying high shearing forceand pressure to accelerate dispersion, but other methods using apropeller-type stirrer, rotary stirrer, electromagnetic stirrer ormanual stirring may also be used. The obtained resin composite may bemolded into the desired shape and used as a molding material. The formof the molding material may be a sheet, pellets or powder.

A resin composite using an elastomer as the resin can be utilized forvarious types of molded resins. The method of producing the molded resinis not particularly restricted, and any of various production methodsmay be used. The molding material may be molded by a desired moldingmethod such as die molding, injection molding, extrusion molding, blowmolding or foam molding to obtain an unvulcanized molded article of thedesired shape. The unvulcanized molded article may then be vulcanized byheat treatment as necessary.

The molded article obtained from the resin composite of this embodimentmay be in any form depending on the purpose, such as a three-dimensionalshape, or a sheet, film or fibrous form. A portion (for example, severallocations) of the molded article may also be melted by heat treatmentand adhered onto a resin or metal substrate. The molded article may alsobe a coated film coated onto a resin or metal substrate, being formed asa laminated body with the substrate. A molded article in a sheet, filmor fibrous form may also be subjected to secondary processing such asannealing treatment, etching treatment, corona treatment, plasmatreatment, texture transfer, cutting or surface-polishing.

In the mixing step for the chemically modified fine fibers and resin,aggregation between chemically modified fine fibers does not occur andthe chemically modified fine fibers homogeneously disperse in the resin,and therefore a resin composite and molded article containing chemicallymodified fine fibers can be obtained that has excellent dynamicproperties, heat resistance, dimensional stability, surface smoothnessand outer appearance. In addition, with the resin composite of thisembodiment it is possible to obtain a satisfactory balance for themechanical properties, including static properties in bending testingand dynamic properties in impact testing. In terms of the heatresistance of the resin composite, the deflection temperature under loadcan be increased by several tens of degrees Celsius. With a moldedarticle that is the final molded product obtained from the resincomposite, the chemically modified fine fibers do not form aggregatedmasses, and therefore the surface smoothness and outer appearance areexcellent.

In terms of the dimensional stability, in particular, when evaluation isconducted based on the linear coefficient of thermal expansion (CTE), itis preferably 80 ppm/k or smaller, more preferably 70 ppm/k or smaller,even more preferably 60 ppm/k or smaller, yet more preferably 55 ppm/kor smaller and most preferably 50 ppm/k or smaller, for the resincomposite of this embodiment.

In terms of the flexural modulus and flexural strength, the proportionof increase in the flexural modulus of the resin composite of thisembodiment, when evaluated as the proportion of increase with respect tothe resin containing no filler component (that is, the chemicallymodified fine fibers and other fillers) is preferably 1.3 or higher,more preferably 1.4 or higher, even more preferably 1.5 or higher, yetmore preferably 1.6 or higher and most preferably 1.7 or higher. Theproportion of increase in the flexural strength of the resin compositeof this embodiment is preferably 1.3 or higher, more preferably 1.4 orhigher, even more preferably 1.5 or higher and most preferably 1.6 orhigher.

In terms of the storage modulus, the proportion of increase in thestorage modulus of the resin composite of this embodiment, whenevaluated as the proportion of increase with respect to the resincontaining no filler component (that is, the chemically modified finefibers and other fillers) is preferably 1.3 or higher, more preferably1.4 or higher, even more preferably 1.5 or higher, yet more preferably1.6 or higher and most preferably 1.7 or higher. The proportion ofincrease in the storage modulus of the resin composite of thisembodiment is preferably 1.3 or higher, more preferably 1.4 or higher,even more preferably 1.5 or higher and most preferably 1.6 or higher.

Second Embodiment

The second embodiment, as one aspect of the invention, provideschemically modified fine cellulose fibers wherein the weight-averagemolecular weight (Mw) is 100,000 or greater, and the ratio (Mw/Mn) ofthe weight-average molecular weight (Mw) and number-average molecularweight (Mn) is 6 or lower. As mentioned above for the first embodiment,since the ends of the cellulose molecules act as origins for thermaldecomposition, a high weight-average molecular weight also results in anarrower molecular weight distribution, resulting in fine cellulosefibers, as well as a resin composite containing the fine cellulosefibers and resin, with high heat resistance.

According to one aspect, the chemically modified fine fibers of thesecond embodiment have an alkali-soluble content of 12 mass % or lower.

According to one aspect, the chemically modified fine fibers of thesecond embodiment have a thermal decomposition initiation temperature(T_(D)) of 270° C. or higher, a number-average fiber diameter of 10 nmor greater and less than 1 μm, and/or a degree of crystallinity of 60%or higher. The chemically modified fine fibers of the second embodimentpreferably have at least one, at least two, at least three, or at leastfour, of the following properties: being esterified fine cellulosefibers; having an average degree of substitution of hydroxyl groups of0.5 or greater; having a mean content for the acid-insoluble componentper unit specific surface area of 1.0 mass %·g/m² or lower; and having acoefficient of variation (CV) for the DS non-uniformity ratio (DSs/DSt),as the ratio of the degree of modification (DSs) of the fiber surfacewith respect to the degree of modification (DSt) of the entire fibers,of 50% or lower. The other aspects of the chemically modified finefibers of the second embodiment are the same as the preferred aspectsfor the chemically modified fine fibers of the first embodimentexplained above.

The second embodiment provides a method for producing chemicallymodified fine cellulose fibers, which includes:

defibrating a cellulose starting material having a weight-averagemolecular weight (Mw) of 100,000 or greater, a ratio (Mw/Mn) ofweight-average molecular weight (Mw) and number-average molecular weight(Mn) of 6 or lower and an alkali-soluble content of 12 mass % or lower,in a dispersion that includes an aprotic solvent, to obtain finecellulose fibers, and

adding a modifying agent-containing solution to the dispersion to modifythe fine cellulose fibers, thereby obtaining chemically modified finecellulose fibers having a weight-average molecular weight (Mw) of100,000 or greater, a ratio (Mw/Mn) of weight-average molecular weight(Mw) and number-average molecular weight (Mn) of 6 or lower, analkali-soluble content of 12 mass % or lower and a degree ofcrystallinity of 60% or higher. According to one aspect, the chemicallymodified fine cellulose fibers obtained by this method have a thermaldecomposition initiation temperature (T_(D)) of 270° C. or higher and anumber-average fiber diameter of 10 nm or greater and less than 1 μm.According to another aspect, the aprotic solvent is dimethyl sulfoxide,and the modifying agent is vinyl acetate or acetic anhydride. Examplesof preferred aspects for defibrating and modification are the same asexplained for the first embodiment.

The second embodiment also provides a resin composite containing thechemically modified fine cellulose fibers and resin, and a method forproducing it. Examples of preferred aspects for the resin composite, itsconstituent components and the method for producing the resin composite,are the same as explained for the first embodiment.

Third Embodiment

The third embodiment, as one aspect of the invention, provides:

a resin composite containing 0.5 to 40 mass % of chemically modifiedfine cellulose fibers and a resin,

wherein the DS non-uniformity ratio (DSs/DSt), as the ratio of thedegree of modification (DSs) of the fiber surfaces with respect to thedegree of modification (DSt) of the entire chemically modified finecellulose fibers, is 1.1 or greater, and the coefficient of variation(CV) of the DS non-uniformity ratio (DSs/DSt) is 50% or lower.

The third embodiment also provides:

a method for producing a resin composite containing 0.5 to 40 mass % ofchemically modified fine cellulose fibers, and a resin, wherein themethod includes:

a defibrating step in which a cellulose starting material is defibratedin a dispersion that includes the cellulose starting material and anaprotic solvent but essentially does not include an ionic liquid orsulfuric acid, to obtain fine cellulose fibers,

a modifying step in which a solution that includes a modifying agent isadded to the dispersion for chemical modification of the fine cellulosefibers, to obtain chemically modified fine cellulose fibers, and

a kneading step in which the chemically modified fine cellulose fibersand the resin are kneaded,

the DS non-uniformity ratio (DSs/DSt), as the ratio of the degree ofmodification (DSs) of the fiber surfaces with respect to the degree ofmodification (DSt) of the entire chemically modified fine cellulosefibers, is 1.1 or greater, and the coefficient of variation (CV) of theDS non-uniformity ratio (DSs/DSt) is 50% or lower.

This method is advantageous for producing a resin composite containingchemically modified fine fibers having a thermal decompositioninitiation temperature (T_(D)) of 270° C. or higher, a number-averagefiber diameter of 10 nm or greater and less than 1 μm and a degree ofcrystallinity of 60% or higher, and a resin.

The other aspects of the resin composite and method for producing itaccording to the third embodiment are the same as the preferred aspectsmentioned above for the resin composite and method for producing itaccording to the first embodiment.

[Uses of Resin Composite]

Because the resin composite of this embodiment has high heat resistanceand light weight, it can substitute for steel sheets, or forfiber-reinforced plastics such as carbon fiber reinforced plastics orglass fiber reinforced plastics, or for inorganic filler-containingresin composites. For example, it can serve as a material for industrialmachinery parts (for example, electromagnetic device housings, rollmaterials, transport arms or medical equipment members), common machineparts, automobile/railway/vehicle parts (for example, outer platings,chassis, aerodynamic members, seats or friction materials fortransmission interiors), ship members (for example, hulls or seats),aviation-related parts (for example, fuselages, wings, tail units,moving vanes, fairings, cowls, doors, seats or interior finishingmaterials), spacecraft, artificial satellite members (motor cases,wings, body frames or antennae), electronic and electrical components(for example, personal computer cases, cellular phone cases, OA devices,AV devices, telephone sets, facsimiles, household electrical appliances,toy parts or printed circuit boards), construction and civil engineeringmaterials (for example, reinforcing steel substitute materials, trussstructures or suspension bridge cables), subsistence items, sports andleisure goods (for example, golf club shafts, fishing rods or tennis andbadminton rackets), and wind power generation housing members, as wellas members of containers and packings, including high-pressurecontainers filled with hydrogen gas or the like to be used for fuelcells.

Preferred among these are members that can exhibit superiority throughhigher heat resistance compared to existing resin composites (i.e.members necessary for resin molding). From this viewpoint, automobilemembers comprising the resin composite of this embodiment and electronicproduct members comprising the resin composite of this embodiment arepreferred.

EXAMPLES

The present invention will now be explained in more specific detailthrough examples, with the understanding that the scope of the inventionis in no way limited to the examples.

Example I: First Embodiment [Production Example 1-1] (Fabrication ofChemically Modified Fine Fibers 1-1)

Using 210 g of filter paper 5A (FILTER PAPER by Advantec Corp.) (meancontent for acid-insoluble component: mass %, alkali-soluble portioncontent: 10.1 mass %) as the starting material for chemically modifiedfine fibers, it was stirred in 5 kg of dimethyl sulfoxide (DMSO) at 500rpm for 1 hour at ordinary temperature, using a uniaxial stirrer (DKV-1(p125 mm dissolver by Aimex Co.). The mixture was then fed to a beadmill (NVM-1.5 by Aimex Co.) using a hose pump and circulated for 120minutes with DMSO alone, to obtain 5.2 kg of defibrated slurry(defibrating step). Also, 572 g of vinyl acetate and 85 g of sodiumhydrogencarbonate were added into the bead mill, and then the mixturewas further circulated for 60 minutes to obtain a defibrated modifiedslurry (defibrating/acetylating step).

During the circulation, the rotational speed of the bead mill was 2500rpm and the circumferential speed was 12 m/s, while the beads used weremade of zirconia with a size of 02.0 mm and the fill factor was 70% (theslit gap of the bead mill was 0.6 mm). During the circulation, theslurry temperature was controlled to 40° C. with a chiller, forabsorption of the heat release by abrasion.

After then adding 10 L of purified water to the obtained defibrated andmodified slurry and thoroughly stirring, it was placed in a dehydratorand concentrated. The obtained wet cake was then re-dispersed in 10 L ofpurified water and stirred and concentrated, and this rinsing procedurewas repeated a total of 5 times to remove the unreacted reagent solvent.The finally obtained aqueous dispersion of chemically modified finefibers 1-1 (solid content: 10 mass %) was vacuum dried at about 40° C.using a revolving/rotating stirrer (V-mini300 by EME Co.) to obtainchemically modified fine fibers 1-1.

FIG. 3 shows a SEM image (magnification: 10,000×) of a porous sheetfabricated by the method described below for the chemically modifiedfine fibers 1-1.

[Production Example 1-2] (Fabrication of Chemically Modified Fine Fibers1-2)

Chemically modified fine fibers 1-2 were obtained in the same manner asProduction Example 1-1, except for using linter pulp as the startingmaterial, and vacuum drying an aqueous dispersion of the obtainedchemically modified fine fibers 1-2 (solid content: 10 mass %) at 40° C.using a revolving/rotating stirrer.

[Production Example 1-3] (Fabrication of Chemically Modified Fine Fibers1-3)

The same method was used as in Production Example 1-2 up to thedefibrating step, except for using the same linter pulp as ProductionExample 1-1 as the starting material, to obtain 5.2 kg of a defibratedslurry (defibrating step). The obtained defibrated slurry was loadedinto an explosion-proof disperser tank, after which 572 g of vinylacetate and 85 g of sodium hydrogencarbonate were added, the internaltemperature of the tank was brought to 40° C., and stirring was carriedout for 120 minutes. The obtained slurry was dispersed and stirred in 10L of purified water, and then concentrated with a dehydrator. Theobtained wet cake was then re-dispersed in 10 L of purified water andstirred and concentrated, and this rinsing procedure was repeated atotal of 5 times to remove the unreacted reagent solvent. Finally, therinsed slurry (solid content: 10 mass %) was vacuum dried at 40° C.using the revolving/rotating stirrer mentioned above, to obtainchemically modified fine fibers 1-3.

[Production Example 1-4] (Fabrication of Chemically Modified Fine Fibers1-4)

Chemically modified fine fibers 1-4 were obtained in the same manner asProduction Example 1-3, except that the stirring time in theexplosion-proof disperser tank was 20 minutes.

[Production Example 1-5] (Fabrication of Chemically Modified Fine Fibers1-5)

Chemically modified fine fibers 1-5 were obtained in the same manner asProduction Example 1-3, except that the stirring time in theexplosion-proof disperser tank was 240 minutes.

[Production Example 1-6] (Fabrication of Chemically Modified Fine Fibers1-6)

After dispersing 4.5 kg of the same linter pulp as Production Example1-2 in 300 L of purified water, the dispersion was stirred forapproximately 30 minutes in a disperser tank, and then the slurry wasbeaten for 30 minutes using a disc refiner with the disc blade gap setto about 1 mm, and further beaten for 120 minutes with the disc bladegap set to 0.1 mm, to obtain a beaten slurry. The obtained beaten slurrywas then treated with a high-pressure homogenizer (corresponding to 10Pass with an operating pressure of 100 MPa), to obtain a CNF slurry(concentration: 1.5 mass %) with a number-average fiber diameter ofabout 75 nm. In order to replace the solvent of the CNF slurry fromwater to dimethylformamide, the CNF slurry was concentrated to a solidcontent of 10 mass % or greater with a dehydrator, after which theconcentrated slurry was loaded into 300 L of dimethylformamide that hadbeen loaded into an explosion-proof disperser tank, and after stirringfor 20 minutes, it was concentrated with a dehydrator to a solid contentof 10 mass % or greater. After carrying out this procedure two moretimes, the re-concentrated slurry was loaded into 150 L ofdimethylformamide in the explosion-proof disperser tank and stirred for30 minutes, after which 15 Kg of acetic anhydride and 5 kg of pyridinewere loaded in, the internal temperature of the tank was brought to 30°C., and stirring was conducted for 120 minutes. The obtained slurry wasdispersed and stirred in 10 L of purified water, and then concentratedwith a dehydrator. The obtained wet cake was then re-dispersed in 10 Lof purified water and stirred and concentrated, and this rinsingprocedure was repeated a total of 5 times to remove the unreactedreagent solvent. The rinsing procedure was repeated 3 times, and theobtained aqueous dispersion of chemically modified fine fibers 1˜4(solid content: 10 mass %) was vacuum dried at 40° C. using therevolving/rotating stirrer mentioned above to produce chemicallymodified fine fibers 1-6.

[Production Example 1-7] (Fabrication of Non-Chemically-Modified FineFibers 1-1)

CELISH KY-100G by Daicel Co. used as non-chemically-modified finecellulose fibers were vacuum dried at 40° C. using therevolving/rotating stirrer mentioned above, to prepare fine fibers 1-1.

[Production Example 1-8] (Fabrication of Chemically Modified Fine Fibers1-7)

After placing 50 g of filter paper 5A (FILTER PAPER by Advantec) in a1000 ml flask, and further adding 300 g of N,N-dimethylacetamide and 300g of ionic liquid 1-butyl-3-methylimidazolium chloride, the mixture wasstirred. Next, 270 g of acetic anhydride was added and reacted, afterwhich the mixture was filtered and the solid content was rinsed. Aftertreatment with a homogenizer, the rinsed slurry (solid content: 10 mass%) was finally vacuum dried at 40° C. using the revolving/rotatingstirrer mentioned above, to prepare chemically modified fine fibers 1-7.

[Example 1-1] (Fabrication of Resin Composite 1-1)

Upon adding 2 parts by mass of the obtained chemically modified finefibers 1-1 and 98 parts by mass of polyamide 66 resin (hereunderreferred to simply as “PA66”) (A226 by Unitika, Ltd.), a mini kneader(“Xplore”, product name of Xplore Instruments) was used for circulatedkneading for 5 minutes at 260° C., 100 rpm (shear rate: 1570 (1/s)),after which it was passed through a die to obtain a (p1 mm strand ofresin composite 1-1. Resin composite pellets obtained from the strand(after cutting the strand to 1 cm lengths) were melted at 260° C. withan accessory injection molding machine, and the resin was used to form adumbbell-shaped test piece conforming to JIS K7127, which was used forevaluations.

[Example 1-2] (Fabrication of Resin Composite 1-2)

Resin composite 1-2 was obtained in the same manner as Example 1-1,except that the amount of chemically modified fine fibers 1-1 waschanged to 4 parts by mass and the amount of PA66 was changed to 96parts by mass.

[Example 1-3] (Fabrication of Resin Composite 1-3)

Resin composite 1-3 was obtained in the same manner as Example 1-1,except that the amount of chemically modified fine fibers 1-1 waschanged to 8 parts by mass and the amount of PA66 was changed to 92parts by mass.

[Example 1-4] (Fabrication of Resin Composite 1-4)

Resin composite 1-4 was obtained in the same manner as Example 1-2,except that the fine fibers were changed to chemically modified finefibers 1-2.

[Example 1-5] (Fabrication of Resin Composite 1-5)

Resin composite 1-5 was obtained in the same manner as Example 1-2,except that the PA66 of Example 1-2 was changed toacrylonitrile-butadiene rubber (DN003 by Zeon Corp.) (hereunder referredto simply as “NBR”), and the kneading temperature in the mini kneaderand the molding temperature in the injection molding machine werechanged to 50° C.

[Example 1-6] (Fabrication of Resin Composite 1-6)

Resin composite 1-6 was obtained in the same manner as Example 1-2,except that the PA66 of Example 1-2 was changed to PA6 (1013B by UbeIndustries, Ltd.) (hereunder referred to simply as “PA6”), and thekneading temperature in the mini kneader and the molding temperature inthe injection molding machine were changed to 240° C.

[Example 1-7] (Fabrication of Resin Composite 1-7)

Resin composite 1-7 in the form of a dumbbell-shaped test piece wasobtained in the same manner as Example 1-1, except that the chemicallymodified fine fibers 1-1 of Example 1-1 were changed to 4 parts by massof chemically modified fine fibers 1-3, the PA66 was changed to 96 partsby mass of a polypropylene resin (Prime Polypro J105G by Prime PolymerCo., Ltd.) (hereunder referred to simply as “PP”), and the kneadingtemperature in the mini kneader and the molding temperature in theinjection molding machine were changed to 160° C.

[Example 1-8] (Fabrication of Resin Composite 1-8)

Resin composite 1-8 in the form of a dumbbell-shaped test piece wasobtained in the same manner as Example 1-1, using a solid mixture(dispersion) (5 parts by mass) of the chemically modified fine fibers1-3 and polyoxyethylene hardened castor oil ether obtained by adding 1part by mass of polyoxyethylene hardened castor oil ether (BLAUNONRCW-20 (hereunder referred to simply as “RCW-20”) by Aoki Oil IndustrialCo., Ltd.) as a dispersion stabilizer with respect to an amount of thechemically modified fine fibers 1-3 corresponding to 4 parts by mass inan aqueous dispersion before drying the chemically modified fine fibers1-3 (solid content: 9 mass %), and using the revolving/rotating stirrermentioned above for kneading at 30° C. for 30 minutes followed by vacuumdrying at about 40° C., and 95 parts by mass of PP, in ProductionExample 1-3.

[Example 1-9] (Fabrication of Resin Composite 1-9)

Resin composite 1-9 was obtained in the same manner as Example 1-8,except that in Example 1-8, the dispersion stabilizer was changed to 1part by mass of DMSO.

[Example 1-10] (Fabrication of Resin Composite 1-10)

Resin composite 1-10 was obtained in the same manner as Example 1-7,except that in Example 1-7, the amount of chemically modified finefibers 1-3 was changed to 8 parts by mass and the amount of PP waschanged to 92 parts by mass.

[Example 1-11] (Fabrication of Resin Composite 1-11)

Resin composite 1-11 was obtained in the same manner as Example 1-8,except that in Example 1-8, a solid mixture comprising 8 parts by massof chemically modified fine fibers 1-3 and 2 parts by mass of RCW-20 (10parts by mass) (as a dispersion) was mixed with 90 parts by mass of PP,and the mixture was melt kneaded.

[Example 1-12] (Fabrication of Resin Composite 1-12)

Resin composite 1-12 was obtained in the same manner as Example 1-9,except that in Example 1-9, a solid mixture comprising 8 parts by massof chemically modified fine fibers 1-3 and 2 parts by mass of DMSO (10parts by mass) (as a dispersion) was mixed with 90 parts by mass of PP,and the mixture was melt kneaded.

[Example 1-13] (Fabrication of Resin Composite 1-13)

Resin composite 1-13 in the form of a dumbbell-shaped test piece wasobtained by melt kneading in the same manner as Example 1-1, using asolid mixture (dispersion) (8 parts by mass) obtained by adding 4 partsby mass of cellulose whiskers (SC900 by Asahi Kasei Corp.) and 2 partsby mass of RCW-20 with respect to an amount of the chemically modifiedfine fibers 1-2 corresponding to 2 parts by mass in an aqueousdispersion before drying the chemically modified fine fibers 1-2 (solidcontent: 10 mass %), and using the revolving/rotating stirrer mentionedabove for kneading at 30° C. for 30 minutes followed by vacuum drying atabout 40° C., and 92 parts by mass of PA66, in Production Example 1-2.

[Example 1-14] (Fabrication of Resin Composite 1-14)

Resin composite 1-14 was obtained by producing 12 parts by mass of asolid mixture in the same manner as Example 1-13, except that 4 parts bymass of a plasticizer (W-260 by DIC Co., Ltd.) instead of RCW-20, and 88parts by mass of PA66, were used in Example 1-13, and then melt kneadingthe mixture.

[Example 1-15] (Fabrication of Resin Composite 1-15)

Resin composite 1-15 was obtained by producing 10 parts by mass of asolid mixture in the same manner as Example 1-13, except that 4 parts bymass of chemically modified fine fibers 1-3 instead of chemicallymodified fine fibers 1-2 and 90 parts by mass of PP instead of PA66 wereused in Example 1-13, and then melt kneading the mixture.

[Example 1-16] (Fabrication of Resin Composite 1-16)

Resin composite 1-16 was obtained by producing 12 parts by mass of asolid mixture in the same manner as Example 1-15, except that 4 parts bymass of W-260 was used instead of RCW-20 in Example 1-15, and then meltkneading the mixture.

[Example 1-17] (Fabrication of Resin Composite 1-17)

Resin composite 1-17 was obtained in the same manner as Example 1-8,except that in Example 1-8, 12 parts by mass of a solid mixturecomprising 10 parts by mass of chemically modified fine fibers 1-2 and 2parts by mass of RCW-20, was mixed with 88 parts by mass of PA6, and themixture was melt kneaded.

[Example 1-18] (Fabrication of Resin Composite 1-18)

Resin composite 1-18 was obtained by producing 10 parts by mass of asolid mixture in the same manner as Example 1-15, except that 90 partsby mass of PA6 was used instead of PP in Example 1-15, and then meltkneading the mixture.

[Example 1-19] (Fabrication of Resin Composite 1-19)

Resin composite 1-19 was obtained in the same manner as Example 1-17,except that the chemically modified fine fibers 1˜4 were used in Example1-17.

[Example 1-20] (Fabrication of Resin Composite 1-20)

Resin composite 1-20 was obtained in the same manner as Example 1-17,except that the chemically modified fine fibers 1-5 were used in Example1-17.

[Comparative Example 1-1] (Fabrication of Resin Composite 1-A)

Resin composite 1-A was obtained in the same manner as Example 1-1,except that the chemically modified fine fibers 1-1 were changed to finefibers 1-1. The resin composite 1-A underwent brown discoloration.

[Comparative Example 1-2] (Resin 1-1)

Resin 1-1 was obtained by casting and cooling PP alone, as a blank,under the same melt molding conditions as in Example 1-7.

[Comparative Example 1-3] (Resin Composite 1-B)

Resin composite 1-B was obtained in the same manner as ComparativeExample 1-2, except that 10 parts by mass of talc was added as a fillercomponent to 90 parts by mass of PP, and the mixture was melt kneaded.

[Comparative Example 1-4] (Resin 1-2)

Resin 1-2 was obtained by casting and cooling PA66 alone, as a blank,under the same melt molding conditions as in Example 1-1.

[Comparative Example 1-5] (Resin Composite 1-C)

Resin composite 1-C was obtained in the same manner as ComparativeExample 1-4, except that 10 parts by mass of talc was added as a fillercomponent to 90 parts by mass of PA66, and the mixture was melt kneaded.

[Comparative Example 1-6] (Resin Composite 1-D)

Resin composite 1-D was obtained in the same manner as Example 1-1,except that the chemically modified fine fibers 1-1 were changed tochemically modified fine fibers 1-6. The resin composite 1-D underwentbrown discoloration.

[Comparative Example 1-7] (Resin Composite 1-E)

Resin composite 1-E was obtained in the same manner as Example 1-2,except that the chemically modified fine fibers 1-1 were changed tochemically modified fine fibers 1-6. The resin composite 1-E underwentbrown discoloration.

[Comparative Example 1-8] (Resin Composite 1-F)

Resin composite 1-F was obtained in the same manner as Example 1-3,except that the chemically modified fine fibers 1-1 were changed tochemically modified fine fibers 1-6. The resin composite 1-F underwentbrown discoloration.

[Comparative Example 1-9] (Resin Composite 1-G)

Resin composite 1-G was obtained in the same manner as Example 1-17,except that the chemically modified fine fibers 1-2 were changed to finefibers 1-1. The resin composite 1-G underwent brown discoloration.

[Comparative Example 1-10] (Resin Composite 1-H)

Resin composite 1-H was obtained in the same manner as Example 1-17,except that the chemically modified fine fibers 1-2 were changed tochemically modified fine fibers 1-6. The resin composite 1-H underwentbrown discoloration.

[Comparative Example 1-11] (Resin Composite 1-I)

Resin composite 1-I was obtained in the same manner as Example 1-17,except that the chemically modified fine fibers 1-2 were changed tochemically modified fine fibers 1-7. The resin composite 1-I underwentbrown discoloration.

Table 1 shows the starting materials and sample compositions for Example1-1 to Example 1-20 and Comparative Examples 1-1 to 1-11.

Example II: Second Embodiment [Example 2-1] (Fabrication of ChemicallyModified Fine Fibers 2-1)

After charging 0.5 kg of linter pulp and 9.5 kg of dimethyl sulfoxide(DMSO) into a KAPPA VITA^(R) rotary homogenizing mixer with a 35 L tanksize, operation was carried out for 4 hours at a rotational speed of6000 rpm, a peripheral speed of 29 m/s and ordinary temperature, fordefibration of the pulp (defibrating step). Next, 0.16 kg of sodiumbicarbonate and 1.05 kg of vinyl acetate were added and operation wascarried out for 2 hours at a rotational speed of 6000 rpm, a peripheralspeed of 29 m/s and 60° C. (defibrating/modifying step). After thenadding 10 L of purified water to the obtained defibrated and modifiedslurry and thoroughly stirring, it was placed in a dehydrator andconcentrated. The obtained wet cake was again dispersed in 10 L ofpurified water and stirred and concentrated, and this rinsing procedurewas repeated a total of 5 times to remove the unreacted reagent solvent,finally obtaining an aqueous dispersion of the chemically modified finefibers 2-1 (number-average fiber diameter: 88 nm) (solid content: 10mass %).

FIG. 4 is a diagram showing a scanning electron microscope (SEM) imageof the chemically modified fine fibers 2-1. The SEM image was takenusing a JSM-6700F by JEOL Corp., under conditions with an accelerationvoltage of 5 kV, 10,000× magnification (the visual field size in FIG. 4is 9 μm x 12 μm) and a WD of 7.1 mm.

[Example 2-2] (Fabrication of Chemically Modified Fine Fibers 2-2)

Chemically modified fine fibers 2-2 (number-average fiber diameter: 65nm) were obtained by production in the same manner as Example 2-1,except that high-purity wood pulp was used as the starting materialinstead of the linter pulp of Example 2-1.

[Example 2-3] (Fabrication of Chemically Modified Fine Fibers 2-3)

Using refined linter pulp as the starting material instead of the linterpulp of Example 2-1, 0.5 kg of the refined linter pulp and 9.5 kg ofDMSO were charged into a KAPPA VITA^(R) rotary homogenizing mixer with atank size of 35 L, and operation was carried out for 4 hours at arotational speed of 6000 rpm, a peripheral speed of 29 m/s and ordinarytemperature, for defibration of the pulp (defibrating step). Next, 0.16kg of sodium bicarbonate and 1.05 kg of vinyl acetate were added andoperation was carried out for 2 hours at a rotational speed of 2500 rpm,a peripheral speed of 12 m/s and 60° C. (modifying step). After thenadding 10 L of purified water to the obtained defibrated and modifiedslurry and thoroughly stirring, it was placed in a dehydrator andconcentrated. The obtained wet cake was again dispersed in 10 L ofpurified water and stirred and concentrated, and this rinsing procedurewas repeated a total of 5 times to remove the unreacted reagent solvent,finally obtaining an aqueous dispersion of the chemically modified finefibers 2-3 (number-average fiber diameter: 80 nm) (solid content: 10mass %).

[Example 2-4] (Fabrication of Chemically Modified Fine Fibers 2-4)

Using 210 g of linter pulp as the starting material for chemicallymodified fine fibers, stirring was carried out for 1 hour at ordinarytemperature with a uniaxial stirrer (DKV-1 φ125 mm Dissolver by AimexCo.) in 5 kg of dimethyl sulfoxide (DMSO) at 500 rpm. The mixture wasthen fed to a bead mill (NVM-1.5 by Aimex Co.) using a hose pump andcirculated for 2 hours with DMSO alone, to obtain 5.2 kg of defibratedslurry (defibrating step). During the circulation, the rotational speedof the bead mill was 2500 rpm and the circumferential speed was 12 m/s,while the beads used were made of zirconia with a size of Φ2.0 mm andthe fill factor was 70% (the slit gap of the bead mill was 0.6 mm). Alsoduring the circulation, the slurry temperature was controlled to 40° C.with a chiller, for absorption of the heat release by abrasion. Theobtained defibrated slurry was then loaded into an explosion-proofdisperser tank, after which 572 g of vinyl acetate and 85 g of sodiumhydrogencarbonate were added, the internal temperature of the tank wasbrought to 40° C., and stirring was carried out for 2 hours (modifyingstep). The obtained slurry was dispersed and stirred in 10 L of purifiedwater, and then concentrated with a dehydrator. The obtained wet cakewas again dispersed in 10 L of purified water and stirred andconcentrated, and this rinsing procedure was repeated a total of 5 timesto remove the unreacted reagent solvent, to obtain chemically modifiedfine fibers 2-4 (number-average fiber diameter: 140 nm).

[Example 2-5] (Fabrication of Chemically Modified Fine Fibers 2-5)

Chemically modified fine fibers 2-5 (number-average fiber diameter: 79nm) were obtained by production in the same manner as Example 2-1,except that filter paper was used as the starting material instead ofthe linter pulp of Example 2-1.

[Example 2-6] (Fabrication of Chemically Modified Fine Fibers 2-6)

Chemically modified fine fibers 2-6 (number-average fiber diameter: 66nm) were obtained by production in the same manner as Example 2-3,except that separate refined linter pulp was used as the startingmaterial instead of the linter pulp of Example 2-3.

[Comparative Example 2-1] (Fabrication of Chemically Modified FineFibers 2-7)

Chemically modified fine fibers 2-7 (number-average fiber diameter: 58nm) were obtained by production in the same manner as Example 2-1,except that wood pulp was used as the starting material instead of thelinter pulp of Example 2-1.

[Comparative Example 2-2] (Fabrication of Chemically Modified FineFibers 2-8)

Chemically modified fine fibers 2-8 (number-average fiber diameter: 73nm) were obtained by production in the same manner as Example 2-1,except that abaca was used as the starting material instead of thelinter pulp of Example 2-1.

[Comparative Example 2-3] (Fabrication of Chemically Modified FineFibers 2-9)

Chemically modified fine fibers 2-9 (number-average fiber diameter: 84nm) were obtained by production in the same manner as Example 2-3,except that different refined linter pulp from the refined linter pulpof Example 2-3 was used.

[Comparative Example 2-4] (Fabrication of Chemically Modified FineFibers 2-10)

Chemically modified fine fibers 2-10 (number-average fiber diameter: 64nm) were obtained by production in the same manner as Example 2-4,except that the circulation time for DMSO alone after feeding to thebead mill as described in Example 2-4 was changed from 2 hours to 8hours.

[Comparative Example 2-5] (Fabrication of Chemically Modified FineFibers 2-11)

After adding 50 g of filter paper and 300 g of1-butyl-3-methylimidazolium chloride as an ionic liquid to 300 ml ofN,N-dimethylacetamide, the mixture was stirred. Next, 270 g of aceticanhydride was added and reacted, after which the mixture was filteredand the solid content was rinsed with water. It was then treated with ahigh-pressure homogenizer to obtain chemically modified fine fibers 2-11(number-average fiber diameter: 44 nm).

[Comparative Example 2-6] (Preparation of Non-Chemically-Modified FineFibers 2-1)

CELISH KY-100G (number-average fiber diameter: 75 nm) by Daicel wereprepared as non-chemically-modified fine cellulose fibers.

The following examples are chemically modified fine fibers of Examples2-1 to 2-6 and Comparative Examples 2-1 to 2-6, or complexes with resinsusing the fine fibers.

[Example 2-7] (Fabrication of Resin Composite 2-1)

Upon adding 2 parts by mass of the obtained chemically modified finefibers 2-1 (as the solid content in the slurry, same hereunder) and 98parts by mass of polyamide 66 resin (hereunder referred to simply as“PA66”) (A226 by Unitika, Ltd.) as resin 2-1, a mini kneader (“Xplore”,product name of Xplore Instruments) was used for circulated kneading for5 minutes at 260° C., 100 rpm (shear rate: 1570 (1/s)), after which itwas passed through a die to obtain a φ1 mm strand of a composite resincomposition. Resin composite pellets obtained from the strand (aftercutting the strand to 1 cm lengths) were melted at 260° C. with anaccessory injection molding machine, and the resin was used to form adumbbell-shaped test piece conforming to JIS K7127, which was used forevaluation. Resin composite 2-1 in the form of the obtaineddumbbell-shaped test piece was used to carry out the appropriateevaluations.

[Example 2-8] (Fabrication of Resin Composite 2-2)

Resin composite 2-2 was obtained in the same manner as Example 2-7,except that the amount of chemically modified fine fibers 2-1 waschanged to 10 parts by mass and the amount of PA66 was changed to 90parts by mass.

[Example 2-9] (Fabrication of Resin Composite 2-3)

Resin composite 2-3 was obtained in the same manner as Example 2-8,except that the PA66 of Example 2-8 was changed to PA6 (1013B by UbeIndustries, Ltd.) (hereunder referred to simply as “PA6”) as the resin2-2, and the kneading temperature in the mini kneader and the moldingtemperature in the injection molding machine were changed to 250° C.

[Example 2-10] (Fabrication of Resin Composite 2-4)

Resin composite 2-4 in different forms of dumbbell-shaped test pieceswas obtained in the same manner as Example 2-7, except that the PA66 ofExample 2-7 was changed to 96 parts by mass of a polypropylene resin(Prime Polypro J105G by Prime Polymer Co., Ltd.) (hereunder referred tosimply as “PP”), as resin 2-3, and the kneading temperature with themini kneader and the molding temperature with the injection moldingmachine were changed to 160° C.

[Example 2-11] (Fabrication of Resin Composite 2-5)

Resin composite 2-5 in different forms of dumbbell-shaped test pieceswas obtained in the same manner as Example 2-7, using a solid mixture(dispersion) (10 parts by mass) of the chemically modified fine fibers2-1 and polyoxyethylene hardened castor oil ether (BLAUNON RCW-20(hereunder referred to simply as “RCW-20”) by Aoki Oil Industrial Co.,Ltd.), obtained by adding 3 parts by mass of RCW-20 as a dispersionstabilizer, with respect to an amount of the chemically modified finefibers 2-1 corresponding to 7 parts by mass in an aqueous dispersionbefore drying the chemically modified fine fibers 2-1 (solid content: 9mass %), and using the revolving/rotating stirrer mentioned above forkneading at 30° C. for 30 minutes followed by vacuum drying at about 40°C., and 90 parts by mass of PA6, in Example 2-7.

[Example 2-12] (Fabrication of Resin Composite 2-6)

Resin composite 2-6 in different forms of dumbbell-shaped test pieceswas obtained in the same manner as Example 2-11, except that in Example2-11, 2 parts by mass of cellulose whiskers (SC900, by Asahi KaseiCorp.) was mixed with the aqueous dispersion of the chemically modifiedfine fibers 2-1 prior to drying and RCW-20 to obtain a solid mixture (12parts by mass), and then the solid mixture (12 parts by mass) and 88parts by mass of PA6 were used.

[Comparative Example 2-7] (Fabrication of Resin Composite 2-7)

Resin composite 2-7 was obtained by fabrication in the same manner asExample 2-9, except that the chemically modified fine fibers 2-1 werechanged to fine fibers 2-1. The resin composite 2-7 underwent browndiscoloration.

[Comparative Example 2-8] (Fabrication of Resin Composite 2-8)

Resin composite 2-8 was obtained by fabrication in the same manner asExample 2-9, except that the chemically modified fine fibers 2-1 werechanged to chemically modified fine fibers 2-7. The resin composite 2-8underwent brown discoloration.

The compositions of the starting materials and samples for the Examplesand Comparative Examples are shown in Table 4.

<Evaluation of Fine Fibers and Resin Composites>

The results of evaluating the properties in Examples I and II are shownbelow in Tables 2, 3 and 5.

(1) Fabrication of Measuring Samples

The chemically modified fine fibers or the fine fibers were evaluatedusing a porous sheet as the measuring sample. A porous sample wasfabricated in the following manner.

First, an aqueous dispersion of the chemically modified fine fibers orthe fine fibers was centrifuged to obtain a condensate (solid content:mass %). Next, the concentrate containing 0.5 g of the chemicallymodified fine fibers or the fine fibers was dispersed in tert-butanol to0.2 mass %, and dispersion treatment was carried out by ultrasonicdispersion until it was free of aggregates. A 100 g portion of theobtained tert-butanol dispersion was filtered on filter paper (5C,Advantech, Inc., diameter: 90 mm) and dried at 150° C., and then thefilter paper was detached to obtain a sheet. Sheets with airpermeability resistance up to 100 sec/100 ml per 10 g/m² basis weight ofthe sheet were considered to be porous sheets, and were used asmeasuring samples.

For the air permeability resistance (sec/100 ml) per 10 g/m² of basisweight of the sheet, the basis weight W (g/m²) of each sample that hadbeen left to stand for 1 day in an environment of 23° C., 50% RH wasmeasured, and then an Oken-type air permeability resistance tester(Model EGO1 by Asahi Seiko Co., Ltd.) was used to measure the airpermeability resistance R (sec/100 ml). The value per 10 g/m² basisweight was calculated by the following formula. Air permeabilityresistance (sec/100 ml) per 10 g/m² basis weight=R/W x 10

(2) Number-Average Fiber Diameter

First, three randomly selected locations on the surface of the poroussheet were observed with a scanning electron microscope (SEM) at amagnification corresponding to 10,000-100,000x, according to the fiberdiameter of the fine fibers. For each of the three obtained SEM images,lines were drawn on the image surface in the weft direction and the warpdirection, the number of fibers crossing the lines and the fiberdiameters of each of the fibers were measured from the magnified image,and the number-average fiber diameters for the warp/weft rows werecalculated for each image. The number average of the number-averagefiber diameter for the 3 images was recorded as the mean fiber diameterof the measured sample.

(3) Specific Surface Area

The BET specific surface area (m²/g) was calculated with the program ofa specific surface area/pore distribution measuring apparatus(Nova-4200e, by Quantachrome Instruments), after drying approximately0.2 g of the porous sheet sample for 2 hours in a vacuum at 120° C. andmeasuring the nitrogen gas adsorption at the boiling point of liquidnitrogen at five points (multipoint method) in a relative vapor pressure(P/P₀) range of 0.05 to 0.2.

(4) IR Index

The infrared spectroscopy spectrum of the porous sheet was measured bythe ATR-IR method, using a Fourier transform infrared spectrometer(FT/IR-6200 by Jasco Corp.). The infrared spectroscopy spectrum wasmeasured under the following conditions.

Number of scans: 64 times,

wavenumber resolution: 4 cm⁻¹,

measuring wavenumber range: 4000 to 600 cm⁻¹,

ATR crystal: diamond,

incident angle: 45°

(4-1) IR index 1370

Based on the obtained IR spectrum, the IR index 1370 was calculatedaccording to the following formula (1):

IR index 1370=H1730/H1370  (1).

In the formula, H1730 and H1370 are the absorbances at 1730 cm⁻¹(absorption band for vibration of the cellulose backbone chain). Therespective baselines used were a line connecting 1900 cm⁻¹ and 1500 cm⁻¹(for H1730) and a line connecting 800 cm⁻¹ and 1500 cm⁻¹ (for H1370),each baseline being defined as the absorbance at absorbance=0.

(4-2) IR Index 1030

Based on the obtained IR spectrum, the IR index 1030 was calculatedaccording to the following formula (2):

IR index 1030=H1730/H1030  (2).

In the formula, H1730 and H1030 are the absorbances at 1730 cm⁻¹ and1030 cm⁻¹ (absorption bands for C—O stretching vibration of thecellulose backbone chain). The respective baselines used were a lineconnecting 1900 cm⁻¹ and 1500 cm⁻¹ and a line connecting 800 cm⁻¹ and1500 cm⁻¹, each baseline being defined as the absorbance atabsorbance=0. The average degree of substitution (DS) was calculatedfrom the IR index 1030 according to the following formula (3):

DS=4.13×IR index 1030  (3).

(5) DS Non-Uniformity Ratio and its Coefficient of Variation (CV)

A 100 g portion of the aqueous dispersion of the chemically modifiedfine fibers (solid content: 10 mass %) was sampled, and 10 g of each wasfrozen and pulverized to prepare 10 powder samples. The powder samplemass was 1 g each. The 10 powder samples were measured by ¹³C solid NMRand XPS, the DSt and DSs of each was determined, and the DSnon-uniformity ratio was calculated for each powder sample. Thecoefficient of variation was calculated using the standard deviation (σ)and arithmetic mean (μ) of the DS non-uniformity ratio for each of theobtained 10 samples.

DS Non-uniformity ratio=DSs/DSt

Coefficient of variation(%)=standard deviation σ/arithmetic mean μ×100

The method of calculating DSt may be subjecting the powder chemicallymodified fine fibers to ¹³C solid NMR measurement, and determining DStaccording to the following formula using the area intensity (Inf) of thesignal (23 ppm) attributed to the carbon atom of —CH3 of the acetylgroup, with respect to the total area intensity (Inp) of the signalsattributed to C1-C6 carbons of the pyranose rings of cellulose,appearing in the range of 50 ppm to 110 ppm.

DSt=(Inf)×6/(Inp)

The conditions used in the ¹³C solid NMR measurement may be as follows,for example. Apparatus: Bruker Biospin Avance 500WB

Frequency: 125.77 MHz

Measuring method: DD/MASLatency time: 75 secNMR sample tube:4 mmφNumber of scans: 640 (˜14 hr)

MAS: 14,500 Hz

Chemical shift reference: glycine (external reference: 176.03 ppm)

As the method of calculating DSs, a powder sample of the chemicallymodified fine fibers used for ¹³C solid NMR measurement was placed on a2.5 mmφ dish-shaped sample stand, the surface was pressed flat and XPSmeasurement was performed. The obtained Cls spectrum was analyzed bypeak separation, and DSs was determined by the following formula usingthe area intensity (Ixf) of the peak (286 eV) attributed to the acetylgroup O—C═O bond with respect to the area intensity (Ixp) of the peakattributed to the C2-C6 carbons of the pyranose rings of cellulose (289eV, C—C bond).

DSs=(I×f)×5/(Ixp)

The conditions used for XPS measurement were the following.

Device: VersaProbe II by Ulvac-Phi, Inc.

Excitation source: mono. AlKa 15 kV×3.33 mAAnalysis size: ˜200 pimpPhotoelectron take-off angle: 45°Capture rangeNarrow scan: C 1s, O 1s

Pass Energy: 23.5 eV (6) Degree of Crystallinity

The porous sheet was subjected to X-ray diffraction and the degree ofcrystallinity was calculated by the following formula.

Degree of crystallinity(%)=[I ₍₂₀₀₎ −I _((amorphous))]/I ₍₂₀₀₎×100

I₍₂₀₀₎: Diffraction peak intensity at 200 plane (20=22.5°) of type Icellulose crystal I_((amorphous)): Amorphous halo peak intensity fortype I cellulose crystal, peak intensity at angle of 4.5° lower thandiffraction angle at 200 plane (20=18.0°).

<X-Ray Diffraction Measuring Conditions>

Apparatus: MiniFlex (Rigaku Corp.)

Operating shaft: 2θ/θ

Source: CuKα

Measuring method: Continuous

Voltage: 40 kV

Current: 15 mA

Initial angle: 2θ=5°

Final angle: 2θ=30°

Sampling width: 0.020°

Scan speed: 2.0°/min

Sample: Porous sheet attached to specimen holder.

(7) Weight-Average Molecular Weight (Mw) and Number-Average MolecularWeight (Mn)

After weighing out 0.88 g of the porous sheet of the chemically modifiedfine fibers or the fine fibers and chopping it into small pieces withscissors, the pieces were gently stirred and allowed to stand for oneday after addition of 20 mL of purified water. The water and solidportion were then separated by centrifugation. After then adding 20 mLof acetone, the mixture was gently stirred and allowed to stand for 1day. The acetone and solid portion were separated by centrifugation.After then adding 20 mL of N,N-dimethylacetamide, the mixture was gentlystirred and allowed to stand for 1 day. Centrifugal separation was againcarried out to separate the N,N-dimethylacetamide and solid content, andthen 20 mL of N,N-dimethylacetamide was added and the mixture was gentlystirred and allowed to stand for 1 day. The N,N-dimethylacetamide andsolid content were separated by centrifugation, 19.2 g of aN,N-dimethylacetamide solution prepared to a lithium chloride content of8 mass % was added to the solid portion, and the mixture was stirredwith a stirrer while visually confirming dissolution. Thecellulose-dissolving solution was filtered with a 0.45 μm filter, andthe filtrate was supplied as a sample for gel permeation chromatography.The apparatus and measuring conditions used were as follows.

Apparatus: Tosoh Corp. HLC-8120

Column: TSKgel SuperAWM-H (6.0 mm I.D.×15 cm)×2

Detector: RI detector

Eluent: N,N-dimethylacetamide (lithium chloride: 0.2%)

Calibration curve: Based on pullulan

(8) Alkali-Soluble Content

The alkali-soluble portion was determined by a method described innon-patent literature (Mokushitsu Kagaku Jikken Manual, ed. The JapanWood Research Society, pp. 92-97, 2000), subtracting the α-cellulosecontent from the holocellulose content (Wise method).

(9) Mean Content for Acid-Insoluble Component and Mean Content forAcid-Insoluble Component Per Unit Specific Surface Area

The acid-insoluble component was quantified by the Klason method,described in non-patent literature (Mokushitsu Kagaku Jikken Manual, ed.The Japan Wood Research Society, pp. 92-97, 2000). The sample of theabsolutely dried chemically modified fine fibers or the fine fibers wasweighed and placed in a prescribed container, 72 mass % concentratedsulfuric acid was added, and the mixture was pressed with a glass roduntil the contents became uniform, after which an autoclave was used todissolve the cellulose and hemicellulose in the acid solution. Thecontents that had been allowed to cool were filtered with glass fiberfilter paper to separate off the acid-insoluble component, which wasquantified to calculate the acid-insoluble component content of thesample. The mean content was calculated as the number-average value for3 samples, and the value was recorded as the mean content for theacid-insoluble component for the chemically modified fine fibers. Themean content for the acid-insoluble component per specific surface area(mass %·g/m²) was calculated from this calculated value.

(10) Thermal Decomposition Initiation Temperature (T_(D)) and 1 wt %Weight Reduction Temperature (T_(1%))

Thermal analysis of the porous sheet was conducted by the followingmethod.

Apparatus: EXSTAR6000 by SII Co.

Sample: Circular pieces cut out from the porous sheet were placed andstacked in an aluminum sample pan, in an amount of 10 mg.

Sample weight: 10 mg

Measuring conditions: Temperature increase from room temperature to 150°C. at a temperature-elevating rate of 10° C./min, in a nitrogen flow of100 ml/min, and holding at 150° C. for 1 hour, followed by cooling to30° C. Subsequent temperature increase from 30° C. to 450° C. at atemperature-elevating rate of 10° C./min.

T_(D) calculation method: Calculation was from a graph with temperatureon the abscissa and weight reduction % on the ordinate. Starting fromthe weight of chemically modified fine fibers at 150° C. (withessentially all of the moisture content removed) (a weight reduction of0 wt %) and increasing the temperature, a straight line was obtainedrunning through the temperature at 1 wt % weight reduction and thetemperature at 2 wt % weight reduction. The temperature at the point ofintersection between this straight line and a horizontal (baseline)running through the origin at weight reduction 0 wt %, was recorded asthe thermal decomposition initiation temperature (T_(D)).

T_(1%) calculation method: The temperature at 1 wt % weight reductionused for T_(D) calculation was recorded as the 1 wt % weight reductiontemperature.

(11) 250° C. Weight Change Rate (T_(250° C.))

Apparatus: EXSTAR6000 by SII Co.

Sample: Circular pieces cut out from the porous sheet were placed andstacked in an aluminum sample pan, in an amount of 10 mg.

Sample weight: 10 mg

Measuring conditions: Temperature increase from room temperature to 150°C. at a temperature-elevating rate of 10° C./min, in a nitrogen flow of100 ml/min, and holding at 150° C. for 1 hour, followed by temperatureincrease from 150° C. to 250° C. at 10° C./min and holding at 250° C.for 2 hours.

T_(250° C.) calculation method: Starting from weight WO as the pointwhere 250° C. was reached, the weight after holding at 250° C. for 2hours was recorded as W1, and calculation was performed by the followingformula.

T _(250° C.)(%):(W1−W0)/W0×100

(12) Change in YI (ΔYI) after Heat Aging

The porous sheet was placed in an oven, and operation was carried outfor 3000 hours at 150° C., atmospheric pressure for heat aging. Thedegree of yellowing of the porous sheet before heat aging and after heataging was evaluated by YI measurement. The YI measurement was carriedout using a CM-700d spectrocolorimeter by Konica Minolta Holdings, Inc.under conditions with reflective mode (SCI+SCE), and a measuringdiameter of 3 mm, and the average value for the YI at 5 arbitrarylocations was determined. The YI before heat aging was subtracted fromthe YI after heat aging to obtain ΔYI.

(13) Sheet Strength after Heat Aging

The porous sheet was placed in an oven, and operation was carried outfor 3000 hours at 150° C., atmospheric pressure for heat aging. A 1cm-wide, 3 cm-long sample strip was cut out from the sample after heataging, and pulled with forceps until it tore. The sheet strength wasevaluated as “Good” if it tore during pulling and resistance was felt bythe hand, the sheet strength was evaluated as “Acceptable” if it toreduring pulling and resistance was not felt by the hand, and the sheetstrength was evaluated as “Poor” if the sample disintegrated at thelocation gripped by the forceps during pulling.

(14) Storage Modulus Change Ratio

The obtained resin composite dumbbell was cut to 4 mm width×30 mm lengthas a measuring sample. Using an EXSTAR TMA6100 viscoelasticity meter(product of SII Nanotechnology, Inc.), the storage modulus was measuredunder a nitrogen atmosphere in tension mode, with a chuck distance of 20mm and a frequency of 1 Hz. In order to relax distortion during moldingof the dumbbell during the measurement, the temperature was increasedfrom room temperature to a high temperature at 5° C./min and thenlowered to 25° C. at 5° C./min and again increased from 25° C. to thehigh temperature at 5° C./min, as the temperature profile, and thestorage modulus change ratio at the time of the second temperatureincrease was measured. The value of the storage modulus at lowtemperature divided by the storage modulus at high temperature wascompared, as the storage modulus change ratio.

For Example I (first embodiment), the low temperature/high temperatureratio was 100° C./200° C. for PA66 and PA6, and 50° C./100° C. for PPand NBR.

For Example II (second embodiment), the low temperature/high temperatureratio was 0° C./150° C. for PA66 and PA6, and −50° C./100° C. for PP.

Generally, the storage modulus is lower at higher temperature, andtherefore the storage modulus change ratio is greater than 1. A valuecloser to 1 may be considered to be lower change in storage modulus athigh temperature, and thus higher heat resistance.

(15) Outer Appearance

The outer appearance of a sample obtained after forming a composite ofthe kneaded resin was evaluated as “Poor” if there were clear burntdeposits (browning), “Good” if no discoloration was visible, or“Acceptable” if there were slight burnt deposits.

(16) Linear Coefficient of Thermal Expansion (CTE)

The resin composite or resin was cut to 3 mm width×25 mm length as ameasuring sample. It was measured using a model SII TMA6100 in tensionmode with a chuck distance of 10 mm and load of 5 g, under a nitrogenatmosphere, raising the temperature from room temperature to 120° C. at5° C./min, lowering the temperature to 25° C. at 5° C./min, and thenagain raising the temperature from 25° C. to 120° C. at 5° C./min. Theaverage linear coefficient of thermal expansion from 30° C. to 100° C.at the time of the second temperature increase was measured.

(17) Flexural Modulus Increase Ratio

An injection molding machine was used to mold an 80 mm×10 mm×4 mm testpiece, and the flexural modulus of each test piece was measuredaccording to ISO178. The obtained flexural modulus was divided by theflexural modulus of the base resin containing no filler component (thatis, cellulose or other filler) to calculate the flexural modulusincrease ratio. That is, the value for a test piece with no increase inflexural modulus was 1.0.

(18) Flexural Strength Increase Ratio

An injection molding machine was used to mold an 80 mm×10 mm×4 mm testpiece, and the flexural strength of each test piece was measuredaccording to ISO178. The obtained flexural strength was divided by theflexural strength of the base resin containing no filler component, tocalculate the flexural strength increase ratio. That is, the value for atest piece with no increase in flexural strength was 1.0.

TABLE 1 Cellulose material Resin material Dispersion stabilizer PartsParts Parts Sample name Name by mass Name by mass Name by mass Example1-1 Resin composite 1-1 Chemically modified fine fibers 1-1 2 PA66 98 —— Example 1-2 Resin composite 1-2 Chemically modified fine fibers 1-1 4PA66 96 — — Example 1-3 Resin composite 1-3 Chemically modified finefibers 1-1 8 PA66 92 — — Example 1-4 Resin composite 1-4 Chemicallymodified fine fibers 1-2 4 PA66 96 — — Example 1-5 Resin composite 1-5Chemically modified fine fibers 1-1 4 NBR 96 — — Example 1-6 Resincomposite 1-6 Chemically modified fine fibers 1-1 4 PA6 96 — — Example1-7 Resin composite 1-7 Chemically modified fine fibers 1-3 4 PP 96 — —Example 1-8 Resin composite 1-8 Chemically modified fine fibers 1-3 4 PP95 RCW-20 1 Example 1-9 Resin composite 1-9 Chemically modified finefibers 1-3 4 PP 95 DMSO 1 Example 1-10 Resin composite 1-10 Chemicallymodified fine fibers 1-3 8 PP 92 — — Example 1-11 Resin composite 1-11Chemically modified fine fibers 1-3 8 PP 90 RCW-20 2 Example 1-12 Resincomposite 1-12 Chemically modified fine fibers 1-3 8 PP 90 DMSO 2Example 1-13 Resin composite 1-13 Chemically modified fine fibers 1-2 2PA66 92 RCW-20 2 Cellulose whiskers SC900 4 Example 1-14 Resin composite1-14 Chemically modified fine fibers 1-2 2 PA66 90 W-260 4 Cellulosewhiskers SC900 4 Example 1-15 Resin composite 1-15 Chemically modifiedfine fibers 1-3 4 PP 90 RCW-20 2 Cellulose whiskers SC900 4 Example 1-16Resin composite 1-16 Chemically modified fine fibers 1-3 4 PP 88 W-260 4Cellulose whiskers SC900 4 Example 1-17 Resin composite 1-17 Chemicallymodified fine fibers 1-2 10 PA6 88 RCW-20 2 Example 1-18 Resin composite1-18 Chemically modified fine fibers 1-3 4 PA6 90 RCW-20 2 Cellulosewhiskers SC900 4 Example 1-19 Resin composite 1-19 Chemically modifiedfine fibers 1-4 10 PA6 88 RCW-20 2 Example 1-20 Resin composite 1-20Chemically modified fine fibers 1-5 10 PA6 88 RCW-20 2 Comp. Example 1-1Resin composite 1-A Fine fibers 1-1 4 PA66 96 — — Comp. Example 1-2Resin 1-1 — — PP 100 — — Comp. Example 1-3 Resin composite 1-B — — PP 90Talc 10  Comp. Example 1-4 Resin 1-2 — — PA66 100 — — Comp. Example 1-5Resin composite 1-C — — PA66 90 Talc 10  Comp. Example 1-6 Resincomposite 1-D Chemically modified fine fibers 1-6 2 PA66 98 — — Comp.Example 1-7 Resin composite 1-E Chemically modified fine fibers 1-6 4PA66 96 — — Comp. Example 1-8 Resin composite 1-F Chemically modifiedfine fibers 1-6 8 PA66 92 — — Comp. Example 1-9 Resin composite 1-G Finefibers 1-1 10 PA6 88 RCW-20 2 Comp. Example 1-10 Resin composite 1-HChemically modified fine fibers 1-6 10 PA6 88 RCW-20 2 Comp. Example1-11 Resin composite 1-I Chemically modified fine fibers 1-7 10 PA6 88RCW-20 2

TABLE 2 Mean content for acid- Mean insoluble content for component perSpecific IR IR DS Non- Degree of acid- unit specific Fiber surface IndexIndex uniformity crystal- insoluble surface area Material diameter area1370 1030 DS ratio CV linity component mass % · Name type Nm M²/g — — —— % % mass % g/m² Prod. Chemically modified Filter 180 15 1.08 0.21 0.871.44 19 75 0.18 0.01 Example 1-1 fine fibers 1-1 paper Prod. Chemicallymodified Linter 65 41 1.05 0.20 0.84 1.39 18 65 4.7 0.11 Example 1-2fine fibers 1-2 Prod. Chemically modified Linter 120 23 1.12 0.22 0.931.31 29 75 4.7 0.20 Example 1-3 fine fibers 1-3 Prod. Chemicallymodified Linter 125 22 0.44 0.05 0.20 1.61 39 81 4.7 0.21 Example 1-4fine fibers 1-4 Prod. Chemically modified Linter 115 24 1.44 0.39 1.401.14 14 71 4.7 0.20 Example 1-5 fine fibers 1-5 Prod. Chemicallymodified Linter 75 36 1.01 0.19 0.79 1.92 51 74 4.7 0.13 Example 1-6fine fibers 1-6 Prod. Fine fibers 1-1 Celish 100 27 — — — — — 82 2.50.09 Example 1-7 Prod. Chemically modified Filter 44 61 1.36 0.31 1.281.05 15 71 0.18 0.003 Example 1-8 fine fibers 1-7 paper

TABLE 3 Thermal 250° C. Storage Outer Flexural Flexural decomposition 1%Weight Weight modulus appearance elasticity strength initiationreduction change Resin change Good, increase increase temperaturetemperature rate material ratio* Acceptable, CTE ratio ratio Name ° C. °C. % — — Poor ppm/k — — Example 1-1 Resin composite 1-1 289 307 −1.2PA66 1.85 Good 68 1.36 1.33 Example 1-2 Resin composite 1-2 289 307 −1.2PA66 1.70 Good 65 1.46 1.40 Example 1-3 Resin composite 1-3 289 307 −1.2PA66 1.61 Good 62 1.51 1.40 Example 1-4 Resin composite 1-4 288 307 −1.3PA66 1.73 Good 66 1.34 1.39 Example 1-5 Resin composite 1-5 289 307 −1.2NBR 1.20 Good 63 1.41 1.42 Example 1-6 Resin composite 1-6 289 307 −1.2PA6 2.12 Good 73 1.44 1.42 Example 1-7 Resin composite 1-7 289 308 −1.1PP 1.92 Good 56 1.62 1.46 Example 1-8 Resin composite 1-8 289 308 −1.1PP 1.76 Good 46 1.68 1.51 Example 1-9 Resin composite 1-9 289 308 −1.1PP 1.79 Good 48 1.80 1.60 Example 1-10 Resin composite 1-10 289 308 −1.1PP 1.80 Good 50 1.91 1.68 Example 1-11 Resin composite 1-11 289 308 −1.1PP 1.76 Good 43 2.00 1.72 Example 1-12 Resin composite 1-12 289 308 −1.1PP 1.80 Good 47 2.10 1.82 Example 1-13 Resin composite 1-13 288 307 −1.3PA66 1.63 Good 42 1.82 1.60 Example 1-14 Resin composite 1-14 288 307−1.3 PA66 1.81 Good 43 1.75 1.55 Example 1-15 Resin composite 1-15 289308 −1.1 PA66 1.48 Good 41 2.33 2.00 Example 1-16 Resin composite 1-16289 308 −1.1 PA66 1.69 Good 43 2.18 1.89 Example 1-17 Resin composite1-17 288 307 −1.3 PA6 1.89 Good 39 1.78 1.70 Example 1-18 Resincomposite 1-18 288 307 −1.3 PA6 1.99 Good 45 1.65 1.65 Example 1-19Resin composite 1-19 271 289 −2.7 PA6 2.01 Acceptable 44 1.43 1.39Example 1-20 Resin composite 1-20 293 309 −1.1 PA6 1.75 Good 33 1.681.71 Comp. Resin composite 1-A 225 243 −16.4  PA66 2.39 Poor 80 1.010.99 Example 1-1 Comp. Resin 1-1 — — — PP 2.43 Good 110 — — Example 1-2Comp. Resin composite 1-B — — — PP 2.20 Good 85 1.12 1.04 Example 1-3Comp. Resin 1-2 — — — PA66 2.50 Good 80 — — Example 1-4 Comp. Resincomposite 1-C — — — PA66 2.29 Good 60 1.22 1.10 Example 1-5 Comp. Resincomposite 1-D 263 281 −3.0 PA66 2.30 Acceptable 77 1.06 1.03 Example 1-6Comp. Resin composite 1-E 263 281 −3.0 PA66 2.25 Acceptable 71 1.16 1.11Example 1-7 Comp. Resin composite 1-F 263 281 −3.0 PA66 2.12 Poor 701.22 1.18 Example 1-8 Comp. Resin composite 1-G 225 243 −16.4  PA6 2.05Poor 65 1.23 1.16 Example 1-9 Comp. Resin composite 1-H 263 281 −3.0 PA62.04 Poor 58 1.27 1.27 Example 1-10 Comp. Resin composite 1-I 269 287−2.8 PA6 2.02 Poor 63 1.20 1.17 Example 1-11 *Rate of change at 100°C./200° C. for PA66 and PA6, rate of change at 50° C./100° C. for PP andNBR

TABLE 4 Alkali- Specific soluble Degree of surface portion crystallinityarea Mw Mw/Mn (mass %) (%) (m²/g) DS Example 2-1 Chemically modified380,000 4.7 3.6 75 36 0.82 fine fibers 2-1 Example 2-2 Chemicallymodified 410,000 3.2 7.1 71 46 0.78 fine fibers 2-2 Example 2-3Chemically modified 190,000 2.4 6.5 65 42 0.95 fine fibers 2-3 Example2-4 Chemically modified 340,000 5.4 3.4 75 22 0.90 fine fibers 2-4Example 2-5 Chemically modified 320,000 2.5 10.5 80 38 0.87 fine fibers2-5 Example 2-6 Chemically modified 160,000 2.0 8.3 64 39 0.97 finefibers 2-6 Comp. Chemically modified 270,000 6.4 18.7 68 49 1.03 Example2-1 fine fibers 2-7 Comp. Chemically modified 600,000 8.7 12.5 62 440.95 Example 2-2 fine fibers 2-8 Comp. Chemically modified 140,000 1.812.2 61 44 1.10 Example 2-3 fine fibers 2-9 Comp. Chemically modified160,000 4.2 4.1 56 50 1.30 Example 2-4 fine fibers 2-10 Comp. Chemicallymodified 280,000 2.2 12.1 77 56 0.95 Example 2-5 fine fibers 2-11 Comp.Non-chemically-modi- 240,000 8.6 10 82 27 0 Example 2-6 fied fine fibers2-1 1% Weight 250° C. reduction weight CV Td Temperature Rate of Sheet(%) (° C.) (° C.) change (%) ΔYI strength Example 2-1 19 290 309 −1.6 22Good Example 2-2 17 273 282 −2.7 29 Good Example 2-3 22 290 309 −1.2 18Good Example 2-4 29 289 308 −1.1 21 Acceptable Example 2-5 24 289 307−1.2 36 Acceptable Example 2-6 25 290 308 −1.1 27 Acceptable Comp. 19258 273 −7.1 42 Poor Example 2-1 Comp. 26 253 266 −3.3 34 Poor Example2-2 Comp. 31 289 307 −1.1 39 Poor Example 2-3 Comp. 19 266 276 −4.8 47Poor Example 2-4 Comp. 27 290 309 −1.0 47 Acceptable Example 2-5 Comp. —225 243 −16.5 65 Poor Example 2-6

TABLE 5 Resin Cellulose Additive Cellulose whiskers Storage Outer PartsParts Parts Parts modulus appear- CTE Sample Name by mass Name by massName by mass Name by mass change* ance ppm/K Example 2-7 Resin PA66 98Chemically 2 7.0 Good 76 composite 2-1 modified fine fibers 2-1 Example2-8 Resin PA66 90 Chemically 10 4.0 Good 30 composite 2-2 modified finefibers 2-1 Example 2-9 Resin PA6 90 Chemically 10 4.5 Good 37 composite2-3 modified fine fibers 2-1 Example 2-10 Resin PP 96 Chemically 4 7.4Good 68 composite 2-4 modified fine fibers 2-1 Example 2-11 Resin PA6 90Chemically 7 RCW-20 3 4.3 Good 33 composite 2-5 modified fine fibers 2-1Example 2-12 Resin PA6 88 Chemically 7 RCW-20 3 SC900 2 4.6 Good 35composite 2-6 modified fine fibers 2-1 Comp. Resin PA6 90 Fine fibers2-1 10 5.3 Poor 50 Example 2-7 composite 2-7 Comp. Resin PA6 90Chemically 10 4.2 Poor 33 Example 2-8 composite 2-8 modified fine fibers2-7 *Change at 0° C./150° C. for PA66 and PA6, change at −50° C./100° C.for PP

Based on the evaluation results for Example I, using chemically modifiedfine fibers with a high thermal decomposition initiation temperature wasfound to yield a resin composite with high heat resistance and excellentouter appearance of the resin composite and excellent mechanicalproperties (storage modulus, CTE, flexural modulus and flexuralstrength). Using chemically modified fine fibers with a low thermaldecomposition initiation temperature, on the other hand, had a highlevel of discoloration and could not yield a resin composite satisfyingall of the physical properties, including outer appearance andmechanical properties.

Based on the evaluation results for Example II, using chemicallymodified fine fibers with a high Mw, low Mw/Mn, low alkali-solubleportion and high degree of crystallinity yielded a resin composite withhigh heat resistance, and excellent outer appearance of the resincomposite, storage modulus and CTE.

Both Examples I and II demonstrated that using resins with high meltingpoints resulted in more excellent outer appearance and resin compositeswith excellent mechanical properties.

INDUSTRIAL APPLICABILITY

The resin composite of the invention can be suitably used as a resincomposite with high heat resistance that is desirable for on-vehicleuse, by using chemically modified fine fibers with a high thermaldecomposition initiation temperature.

1-33. (canceled)
 34. Chemically modified fine cellulose fibers whereinthe weight-average molecular weight (Mw) is 100,000 or higher, the ratio(Mw/Mn) of the weight-average molecular weight (Mw) and number-averagemolecular weight (Mn) is 6 or lower, the alkali-soluble portion contentis 12 mass % or lower and the degree of crystallinity is 60% or higher.35. The chemically modified fine cellulose fibers according to claim 34,wherein the thermal decomposition initiation temperature (T_(D)) is 270°C. or higher and the number-average fiber diameter is 10 nm or greaterand less than 1 μm.
 36. The chemically modified fine cellulose fibersaccording to claim 34, which are esterified fine cellulose fibers. 37.The chemically modified fine cellulose fibers according to claim 34,wherein the average degree of substitution of hydroxyl groups is 0.5 orgreater.
 38. The chemically modified fine cellulose fibers according toclaim 34, wherein the coefficient of variation (CV) of the DSnon-uniformity ratio (DSs/DSt), as the ratio of the degree ofmodification (DSs) of the fiber surface with respect to the degree ofmodification (DSt) of the entire chemically modified fine cellulosefibers, is 50% or lower.
 39. The chemically modified fine cellulosefibers according to claim 34, wherein the average content of theacid-insoluble component per unit specific surface area of thechemically modified fine cellulose fibers is 1.0 mass %·g/m² or lower.40. A method for producing chemically modified fine cellulose fibers,which includes: defibrating a cellulose starting material having aweight-average molecular weight (Mw) of 100,000 or greater, a ratio(Mw/Mn) of weight-average molecular weight (Mw) and number-averagemolecular weight (Mn) of 6 or lower and an alkali-soluble content of 12mass % or lower, in a dispersion that includes an aprotic solvent, toobtain fine cellulose fibers, and adding a modifying agent-containingsolution to the dispersion to modify the fine cellulose fibers, therebyobtaining chemically modified fine cellulose fibers having aweight-average molecular weight (Mw) of 100,000 or greater, a ratio(Mw/Mn) of weight-average molecular weight (Mw) and number-averagemolecular weight (Mn) of 6 or lower, an alkali-soluble content of 12mass % or lower and a degree of crystallinity of 60% or higher.
 41. Aresin composite containing 0.5 to 40 mass % of chemically modified finecellulose fibers and a resin, wherein the DS non-uniformity ratio(DSs/DSt), as the ratio of the degree of modification (DSs) of the fibersurfaces with respect to the degree of modification (DSt) of the entirechemically modified fine cellulose fibers, is 1.1 or greater, and thecoefficient of variation (CV) of the DS non-uniformity ratio (DSs/DSt)is 50% or lower.
 42. The resin composite according to claim 41, whereinthe chemically modified fine cellulose fibers have: a thermaldecomposition initiation temperature (T_(D)) of 270° C. or higher, anumber-average fiber diameter of 10 nm or greater and less than 1 μm,and a degree of crystallinity of 60% or higher.
 43. The resin compositeaccording to claim 41, wherein the resin is a thermoplastic resin. 44.The resin composite according to claim 41, wherein the melting point ofthe resin is 220° C. or higher.
 45. The resin composite according toclaim 41, wherein the weight-average molecular weight (Mw) of thechemically modified fine cellulose fibers is 100,000 or greater, and theratio (Mw/Mn) of the weight-average molecular weight (Mw) andnumber-average molecular weight (Mn) is 6 or lower.
 46. The resincomposite according to claim 41, wherein the average degree ofsubstitution of hydroxyl groups of the chemically modified finecellulose fibers is 0.5 or greater.
 47. The resin composite according toclaim 41, wherein the chemically modified fine cellulose fibers areesterified fine cellulose fibers.
 48. The resin composite according toclaim 41, wherein the content of the alkali-soluble portion of thechemically modified fine cellulose fibers is 12 mass % or lower.
 49. Theresin composite according to claim 41, wherein the average content ofthe acid-insoluble component per unit specific surface area of thechemically modified fine cellulose fibers is 1.0 mass %·g/m² or lower.50. A resin composite containing 0.5 to 40 mass % of chemically modifiedfine cellulose fibers according to claim 34, and a resin.
 51. A methodfor producing a resin composite containing 0.5 to 40 mass % ofchemically modified fine cellulose fibers, and a resin, wherein themethod includes: a defibrating step in which a cellulose startingmaterial is defibrated in a dispersion that includes the cellulosestarting material and an aprotic solvent but essentially does notinclude an ionic liquid or sulfuric acid, to obtain fine cellulosefibers, a modifying step in which a solution that includes a modifyingagent is added to the dispersion for chemical modification of the finecellulose fibers, to obtain chemically modified fine cellulose fibers,and a kneading step in which the chemically modified fine cellulosefibers and the resin are kneaded, the DS non-uniformity ratio (DSs/DSt),as the ratio of the degree of modification (DSs) of the fiber surfaceswith respect to the degree of modification (DSt) of the entirechemically modified fine cellulose fibers, is 1.1 or greater, and thecoefficient of variation (CV) of the DS non-uniformity ratio (DSs/DSt)is 50% or lower.
 52. A method for producing a resin composite accordingto claim 41, wherein the method includes: a step of defibratingcellulose in a dispersion containing a cellulose starting material witha cellulose purity of 85 mass % or greater, and an aprotic solvent, toobtain fine cellulose fibers, a step of adding a solution containing amodifying agent to the dispersion to modify the fine cellulose fibers,thereby obtaining chemically modified fine cellulose fibers having athermal decomposition initiation temperature (T_(D)) of 270° C. orhigher, a number-average fiber diameter of 10 nm or greater and lessthan 1 μm, and a degree of crystallinity of 60% or higher, and a step ofmixing the chemically modified fine cellulose fibers with a resin. 53.The method according to claim 51, wherein the aprotic solvent isdimethyl sulfoxide, and the modifying agent is vinyl acetate or aceticanhydride.
 54. The method according to claim 52, wherein the aproticsolvent is dimethyl sulfoxide, and the modifying agent is vinyl acetateor acetic anhydride.
 55. A member for an automobile, comprising a resincomposite according to claim
 41. 56. A member for an automobile,comprising a resin composite according to claim
 50. 57. A member for anelectronic product, comprising a resin composite according to claim 41.58. A member for an electronic product, comprising a resin compositeaccording to claim 50.